We have used a recently developed model for s.c. abscess formation to study the effect of corticosteroids on abscess formation in mice. Mice were given daily i.p. injections of either hydrocortisone, 20 mg/kg/day or dexamethasone, 0.8 mg/kg/day, starting 3 days before inoculation with Staph, aureus and continuing for the duration of the experiment. Another group of mice was given a single injection of dexamethasone, 8 mg/kg, 1 h after inoculation with Staph. aureus. Encapsulated abscesses developed in all animals by Day 4, and there was no mortality. Abscess volume +/- s.l. mean at 4 days was reduced (p less than 0.0005) from 39.9 +/- 3.0 mm3 in controls to 16.7 +/- 3.6 mm3 in the daily dexamethasone group. Abscess volume at 4 days after a single dose of dexamethasone was 39.9 +/- 8.0 mm3. Bacterial concentrations per ml of pus were equivalent in all groups (10(10,6)-10(10.9). The effect of steroids on formation of sterile abscesses was also studied. Abscess volumes were smaller in animals given daily hydrocortisone or dexamethasone when compared to controls, but the difference was significant only for mice receiving daily hydrocortisone. These results suggest that prolonged high-dose steroid administration decreased the magnitude of the acute inflammatory reaction responsible for abscess formation in the soft tissue but did not interfere significantly with the process of containment and encapsulation of s.c. abscesses. A single massive dose of steroid did not influence abscess formation.