The effect of theophylline treatments on the activity of carnitine palmitoyltransferase (CPT) in skeletal muscle and the liver of rats was investigated. Theophylline was administered at 100 mg/kg bw/day and effects were monitored after a treatment period that lasted between a week and five weeks. Results showed that a significant increase in the activity of CPT was observed in skeletal muscle of theophylline-treated groups as compared to either control or placebo groups. However, there was no significant change in the activity of CPT in the hepatic tissues of theophylline-treated groups. The observed discrepancies in activity of CPT might be due to the presence of two isoenzymes, the muscle type (M-CPT) and liver type (L-CPT); it is possible that theophylline affects only M-CPT activity.