We report the case of a 47-year-old woman with a history of mitral valve replacement with a mechanical prosthesis who was admitted to the hospital with a 3-month history of progressive exertional dyspnoea and was diagnosed as suffering from prosthetic valve thrombosis. Two consecutive courses of streptokinase were given as an intravenous infusion over 90 min at a dose of 1,500,000 IU each. Twenty minutes after the start of the second infusion (3 h and 20 min after the first one) she developed chills, fever, tachycardia and hypotension: symptomatic treatment was given and the infusion was completed. Two days later jaundice and choluria appeared with laboratory findings of hepatic cytolysis and cholestasis and renal insufficiency. The results of extensive microbiological and immunological investigations were not revealing. All the laboratory values spontaneously returned to baseline levels over the next 4 weeks. These abnormalities were attributed to an allergic reaction to streptokinase, although the exact pathogenic mechanisms involved are not known. We believe that further studies to elucidate the mechanism involved in the production of these effects are warranted in view of their potential clinical severity.