Two patients hyperinfected with Strongyloides stercoralis (an intestinal nematode) are described. Both were both in Puerto Rico and had left the island six to 15 years previously; both were receiving adrenal steroids (one for Hodgkin's disease and the other for Goodpasture's syndrome). One died shortly after diagnosis, but the other survived the hyperinfection syndrome and complicating bacterial sepsis and meningitis. In addition to our case reports, 103 previously described cases of presumed strongyloides hyperinfection are reviewed. Among 89 patients immunocompromised by therapy or disease, the mortality rate was 86%; bacterial sepsis often contributed to the fatal outcome. In most cases, infection was acquired in an endemic area, sometimes long before the hyperinfection syndrome occurred. The few patients who had never been to an endemic area had a history of prolonged contact with highly soiled material, an observation suggesting cross infection from a contaminated person. When administered in time, thiabendazole, the drug of choice for strongyloidiasis, was effective in 70% of cases. If intestinal infection with S. stercoralis is detected and treated before immunosuppressive therapy is initiated and if a high index of suspicion for the hyperinfection syndrome is maintained while immunosuppressive therapy is given, the mortality from this disease should decrease.