The pharmacokinetics of potassium penicillin G were studied in both healthy (n = 8) and experimentally Streptococcus-suis-infeaed (n = 6) pigs following intramuscular administration (15 000 iu/kg). Streptococcus-suis infection was induced artificially in young cross-bred pigs by subcutaneous inoculation with 9 × 108 to 109 colony-forming units of S. suis. The rectal temperature of infected pigs was significantly increased (P < 0.01) before penicillin G injection and this was maintained for 8 h after the drug was given. Other clinical symptoms were also present. The serum concentration-time data for penicillin were found to fit a one-compartment open model with first-order absorption in the two groups of pigs. Significant changes were not observed between healthy and diseased pigs in following parameters: A, Ka, Ke and Tmax-However, in diseased pigs, significant increases (P < 0.01) were found in Vd and ClB, and significant decreases (P < 0.01) in Cmax and AUC occurred. The increased body clearance (ClB) and greater apparent volume of distribution (Vd) of penicillin G could partly explain why the serum values of the drug were much lower in diseased pigs than in healthy pigs.