To evaluate the efficacy (stool frequency) and safety (adverse experiences) of albendazole, administered for 28 days, compared to placebo and for 62 days in open-label fashion, in treating intestinal microsporidiosis in HIV-positive patients. To assess the effect of albendazole on stool volume, weight gain, microsporidial counts in small bowel biopsies, and on the relationship between microsporidial counts in stool and stool frequency and volume. To correlate microsporidial counts with the clinical course of microsporidiosis.