Even though cellular mechanisms producing insulin resistance (IR) remain unclear, the presence of IR is strongly predictive of the increased risk in development of type 2 diabetes (T2D) (1-4). Skeletal muscle plays a major role in the development of IR and progression to T2D (1, 3,4). Potential roles and mechanisms for alterations of intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) and lipid saturation index in muscles of different fiber type distributions in relation to the development of IR and T2D have been investigated by several researchers (1, 3-7). Using PRESS and STEAM-based single- and multi-voxel localized one-dimensional (1D) MR spectroscopy (MRS), previous research has focused mainly on investigating IMCL and EMCL levels (1, 5-7). It has been shown that acetylcarnitine is formed in conditions in which acetyl-CoA formation, either as an end product of glycolysis or b-oxidation, exceeds its entry into the tricarboxylic (TCA) cycle; free carnitine can act as a sink for excess acetyl groups in a reversible reaction catalyzed by the enzyme carnitine acetyltransferase (CRAT). Boss et al. and Ren et al. independently demonstrated the detection of carnitine and acetylcarnitine resonances after exercise using proton MRS (8-9). Recently, Lindeboom et al. reported that measuring acetylcarnitine concentrations using 1H-MRS is feasible in the skeletal muscle without exercise using long TE of 350ms on clinical MR scanners and their results demonstrated a reciprocal distribution with mean concentrations of acetylcarnitine in the vastus lateralis muscle correlating with mean insulin sensitivity in each of the four different groups including T2D, obese, endurance trained and lean healthy subjects (10). Hence, a major goal of this work was to investigate acetylcarnitine levels in different regions of human thigh and calf muscles using the long TE-based PRESS.We have studied five healthy volunteers (mean age of 29.2 years) and one diabetic type 2 patient (61 years old) so far. A Siemens 3T Prisma MRI scanner equipped with a 2-channel body ‘transmit’ coil was used in combination with a 4-channel flexible phased-array combined with selected channels of a spine MRI ‘receive coil’ for the thigh muscle. A 15-channel transmit/receive coil was used for the calf muscle investigation. Right thigh and right calf muscles were chosen for the MRS scan. Axial T1-weighted MR images were used to select a volume of interest (VOI) from which the 1D MRS was acquired. The PRESS sequence (11) was used using the following acquisition parameters: TR/TE=6s/350ms, 64 averages, and a voxel volume of 4x4x3cm3 At this long TE, water suppression was not used. A larger voxel was used to compensate for the signal loss due to long TE. Manual shim was performed and the FWHM of water peak was approximately 25Hz. The muscle spectra were processed on TARQUIN software (12).Fig.1 shows the axial T1 weighted MRI showing the PRESS VOI localization in the vastus muscle. Fig.2 shows a long TE spectrum with enhanced visibility of the acetylcarnitine peak at 2.13 ppm in the vastus muscle of a 25 year-old healthy male subject and also, the long TE MRS of a 61 year-old male diabetic patient in vastus muscle. The trimethylamine (TMA) peak of acetylcarnitine was overlapping with total choline groups. Compared to the lean young healthy control, the thigh muscle spectrum of the 61 year-old T2D patient showed decreased level of acetylcarnitine. There were other peaks due to EMCL and IMCL of poly-methylene protons and methyl protons of saturated/unsaturated lipid pool, Cr/PCr, residual water and olefenic/glycogen moieties. Fig.3 shows the long TE MR spectrum recorded in the mixed medial hip adductr and posterior knee flexor muscle regions of the same 25 year-old healthy subject whose vastus muscle data is presented in Figs.1-2. An axial T1-weighted calf MRI of a 38 year-old healthy male and the calf muscle long TE spectrum are presented in Fig.4. At short TE (30ms), the acetylcarnitine peak was hardly visible due to broad lipid resonances in the region of 2.0 to 2.5 ppm. Also very characteristic for the long-TE spectrum was the sharp, single, and symmetric appearance of the total creatine peak. Our pilot findings showing acetylcarnitine without exercise are in agreement with the previous study by Lindeboom et al. (10). However, there were varying levels of acetylcarnitine in different muscles of healthy subjects.These results demonstrate our initial experience in evaluating PRESS-localized long TE spectra in different regions of the thigh and calf muscles monitoring acetylcarnitine, IMCL, EMCL, creatine, trimethylamines and carnosine. Future efforts will focus on evaluating the MRS technique in larger cohorts of endurance trained and lean young healthy, obese and T2D patients.