Three corticosteroid products (triamcinolone acetonide, fluocinonide, betamethasone valerate) and a control product composed of water, petrolatum, mineral oil, cetyl alcohol, steryl alcohol, sodium lauryl sulfate, cholesterol, and methylparaben each were applied topically to healthy dogs (5 dogs/product) once daily for 5 consecutive days. Plasma concentrations of immunoreactive adrenocorticotropic hormone (iACTH) and cortisol were determined before 1 microgram of ACTH/kg of body weight was given intravenously (pre-ACTH values) and cortisol was again measured 60 minutes after ACTH was given (post-ACTH values). Cortisol and iACTH concentrations were determined in each dog before, during, and after administration of the corticosteroid products. All 3 corticosteroids caused prompt and sustained pituitary-adrenocortical suppression. Compared with control applications, the application of corticosteroids resulted in significant reduction of plasma cortisol and iACTH concentrations by day 2 of treatment, and the lower concentrations continued to day 5. One week after the last application of the corticosteroids, plasma iACTH concentrations in the corticosteroid-treated dogs had returned to the range of values for the control dogs; however, pre- and post-ACTH cortisol concentrations remained suppressed in all corticosteroid-treated dogs. Two weeks after the last treatment, the pre-ACTH plasma cortisol concentrations of corticosteroid-treated dogs returned to those of the control dogs, but the post-ACTH plasma cortisol concentrations remained suppressed. By 3 weeks after the last treatment, post-ACTH plasma cortisol concentrations of dogs treated with triamcinolone acetonide had returned to the range of values for the control dogs, but remained suppressed in the other 2 groups of dogs. All indices of pituitary-adrenocortical activity were within the control range by 4 weeks after the last treatment.(ABSTRACT TRUNCATED AT 250 WORDS)