The effects of terfenadine and pseudoephedrine, alone and in combination, have been assessed in a nasal provocation test and in perennial rhinitis. In a double-blind, placebo-controlled cross-over nasal provocation test, twelve men allergic to grass pollen were treated with two daily doses of placebo, terfenadine 60 mg, pseudoephedrine 120 mg, or the combination of the two, for 2 days preceding each test. The allergic reaction threshold, based on rhinorrhoea, sneezing and nasal inspiratory peak flow rate, was raised significantly both by terfenadine and pseudoephedrine, and their effects appeared additive (repeated measures analysis of variance). In a double-blind, randomized clinical study of perennial rhinitis two parallel groups, the efficacy and tolerability of terfenadine and terfenadine-pseudoephedrine were compared in 50 patients. Symptoms and signs in both groups were improved after 14 days of treatment. Differences between groups showed a trend in favour of terfenadine-pseudoephedrine, for swelling of the nasal mucosa (rhinoscopy) they were statistically significant. Both medications were well tolerated overall, although adverse events and reactions were more frequent in the terfenadine-pseudoephedrine group. In conclusion, terfenadine-pseudoephedrine and its constituents taken alone were effective. The combination performed better, but adverse events were somewhat more frequent with the combination than with terfenadine alone.