In this study the effect of acidic beverages (Pepsi ) on the bioavailability of theophylline was invest igated in healthy rabbits. Assuming an open one compartment model, th eophylline suspension (100mg/kg) was administered o rally via intragastric tube. Blood samples were withdrawn at time intervals from 0-24hr. after washing period of 7 days, Pepsi (10ml/kg) was administered concomitantly with theophylline (100mg/kg) and then blood samples wer e taken at similar intervals. Plasma was separated and trea ted in a specific manner and assayed for theophylli ne by using high performance liquid chromatography (HPLC). The data calibration curve was constructed and various pharmacokinetic parameters were calculated. Compari sons of data revealed significant differences betwe en the pharmacokinetic parameters for theophylline given a lone and with pepsi. The results suggest a signific ant increase in the bioavailability of theophylline in presence of pepsi that ultimately will lead to the appearanc e of unwanted side effect and toxic response.