In a prospective study, 29 patients were observed over a period of 42 weeks for signs of oral candidosis (OC), immunological parameters and other typical AIDS-related events. Before the study started, no OC was observed in any of the patients. During the observation period, OC was diagnosed in 12 of the 29 patients (41%). 5 of these 12 patients (42%) developed full-blown AIDS during the 42 weeks. In contrast, a progression to AIDS was observed in only 1 of the 17 patients (5.9%) without OC. The laboratory findings for patients with and without OC showed statistically significant differences for neopterin (23.6 against 14.4 nmol l-1), CD4 counts (417 against 763/mm3) and CD4/CD8 ratios (0.45 against 0.85). Based on these results, it seems justifiable to consider prophylactic measures such as pentamidine inhalation and/or treatment with zidovudine in HIV-infected patients with immunodeficiency and occurrence of OC.