In 1990 and 1991 we operated on 2 patients with persistent clinical hemolysis, in the absence of perivalvular leaks, who had had their mitral valves replaced with St. Jude Medical valve (SJMV) prostheses. The valves had been implanted 14 months and 3 months before, respectively. There were no other discernible causes for the hemolysis and when each SJMV was replaced the hemolysis disappeared in that patient. The first valve was not tested in the laboratory owing to its loss, but it looked normal. The second valve was tested and found to have regurgitation well within the usual limits for this valve. Fringe pattern interferometry indicated that the leading edge of each leaflet was flatter and less smooth than that of another SJMV. Reviewing the literature we find that idiopathic, persistent clinical hemolysis in recipients of St. Jude mechanical heart valves is a rare phenomenon, which has appeared in 4 reports totaling 9 cases. We discuss the suggested mechanisms involved, and add the possibility of leading leaflet edge characteristics.