1. The aim of my study was to find the effect of co-administrating orange juice and hesperidin on the bioavailability of metoprolol tartrate in rabbits. 2. Metoprolol tartrate (10mg/kg) was given orally to rabbits with hesperidin (10mg/Kg) and with orange juice (6ml/Kg) separately. 3. The plasma concentrations of metoprolol tartrate was determined using Reverse Phase-High Performance Liquid Chromatography at 1.5, 1, 2, 4 and 6 hours and the pharmacokinetic parameters were studied. 4. In comparison to the control group, the AUC of metoprolol tartrate was increased significantly by 68.32% with hesperidin while orange juice substantially reduced the AUC by 37.08% .However no significant change was observed in T_max K_el and Vd in both groups. The relative bioavailability of metoprolol tartrate with hesperidin was 168.3% as compared to orange juice i-e 62.9%. 5. The present study revealed that the concurrent intake of hesperidin with metoprolol tartrate increased its bioavailability while orange juice administration suppressed its bioavailability. The change in bioavailability of metoprolol tartrate might be due to alterations in the activity of cytochrome P450 enzymes involved in the metabolism of metoprolol tartrate. However, the exact mechanism is still not known. These interactions may be of clinical significance.