396 We have shown that neither [lactate] nor cross-sectional area (XSA) changes are necessary for 1H T2 changes during exercise (Damon et al., 1996. Proc. XVIIth ICMRBS, p. 140). In this study we expanded on these findings by measuring the effect of isometric contraction on T1, intra- and extra- cellular T2 (T2,I and T2,E), the% of total tissue water that is cellular (%TTWI), [lactate], and XSA. Frog gastrocnemius muscles were stimulated (one 1s maximal isometric contraction/minute for 60 min.) and measured the above-named variables by1 H NMR/MRI. Three treatments (Ringer's, Ringer's + 2.0mM NaCN, Ringer's+ 0.5mM Iodoacetic Acid (IAA)) were used to permit, enhance, or inhibit lactate production and decouple lactate effects from other effects of exercise. Control muscles were similarly treated, but not stimulated. To date, four muscles have been used in each treatment group (12 total), and 3 in each control group (9 total). Preliminary data indicate that, in accord with our previous findings, [lactate] and XSA rise in stimulated NaCN-treated and untreated muscles and that neither of these variables changes in stimulated IAA-treated muscles. T2,I increases following stimulation under each treatment, but%TTWI, T1, and T2,E do not appear to change under any type of metabolic inhibition. In control muscles, preliminary data indicate the stability of all variables over a 60 min. period. These data, in combination with our previous findings, suggest that: 1) changes in [lactate], XSA, and%TTWI, are not necessary for exercise-induced T2 changes; 2) these intramuscular changes are not sufficient to increase T1 during exercise; and 3) T2 changes can result from solely intramuscular, and probably intracellular, factors.