A group of 75 subjects with asthma requiring daily corticosteroids for control were enrolled in a 2-yr, double-blind, placebo-controlled study of the use of troleandomycin combined with methylprednisolone, compared with methylprednisolone alone, for the management of their asthma. The primary outcome variables were determination of the lowest stable methylprednisolone dose and assessment of corticosteroid side effects. Methylprednisolone dose was adjusted to maintain optimal control of asthma symptoms. A total of 30 patients receiving TAO and 27 patients receiving placebo completed 1 yr; 17 on TAO and 8 on placebo completed 2 yr of double-blind participation. Control of asthma was equivalent in both groups. The vast majority of patients in both groups achieved alternate-day dosing (29 of 30 on TAO and 23 of 27 on placebo in the first year). The lowest stable doses of methylprednisolone achieved were 10.4 mg/day (placebo) versus 6.3 mg/day (TAO) in the 1-yr group (p = 0.03). However, the baseline dose was also significantly higher in the placebo group (22.8 versus 17.6 mg/day in the TAO group). Therefore, the reductions in methylprednisolone dose were not significantly different between treatment groups. Differences were observed between the two treatment groups in serum IgG, fasting blood sugar, serum cholesterol, and progression of osteoporosis. In each instance the more unfavorable response occurred in those subjects receiving TAO. We conclude that the addition of TAO to methylprednisolone was not accompanied by a reduction in corticosteroid side effects compared with treatment with methylprednisolone alone. Furthermore, no evidence was found for a subset of "TAO responders."(ABSTRACT TRUNCATED AT 250 WORDS)