1. Exposure of isolated skeletal muscle to troglitazone has resulted in inconsistent findings ranging from inhibition to stimulation of fuel oxidation and the glycogenic pathway. To better understand such variation in outcome, the present study used isolated rat soleus muscle strips to examine the interdependent influences of prolonged maintenance in vitro and of troglitazone exposure. 2. If freshly isolated muscle strips were exposed to troglitazone (1 micro mol l(-1)) for 24 h, glucose oxidation was markedly reduced (-26+/-1%, P<0.0001), whereas glycogen synthesis remained unaffected (+9+/-7%, n.s.). 3. In contrast, extended exposure to troglitazone for 72 h increased both glucose oxidation (+65+/-28%, P<0.05) and glycogen synthesis (+46+/-11%, P<0.005), and a similar stimulatory effect was also observed in muscles exposed to troglitazone only during the last 24 h of their 72 h preincubation period (glucose oxidation: +61+/-15%, P<0.001; glycogen synthesis: +43+/-15%, P<0.01). 4. Troglitazone thus stimulated glucose utilization in long-term incubated muscle independent of the duration of exposure (24 or 72 h), whereas it inhibited glucose utilization in freshly isolated muscle. 5. The observed differences in troglitazone action on freshly isolated vs long-term incubated muscle suggest that findings on muscle tissue subject to prolonged maintenance in vitro cannot be extrapolated to native muscle in vivo.