The efficacy and safety of an extended-release combination of loratadine plus pseudoephedrine sulfate (SCH 434) was compared with that of a tablet containing chlorpheniramine maleate plus pseudoephedrine sulfate (CTM-D) in 131 patients with symptomatic seasonal allergic rhinitis. Patients were randomly assigned to receive either SCH 434 (loratadine 5 mg and pseudoephedrine sulfate 120 mg) or CTM-D (chlorpheniramine maleate 12 mg and pseudoephedrine sulfate 120 mg) twice daily for 2 weeks. Evaluations were made after 3, 7, and 14 days of treatment. Demographics (age, race, sex, and duration of seasonal allergic rhinitis) and baseline total symptom scores were comparable between groups. Both combination products were effective in relieving the symptoms of allergic rhinitis. Improvement in total symptom scores was 54% on day 3 and 65% on day 14 in the SCH 434 group versus 57% on day 3 and 64% on day 14 in the CTM-D group. Individual symptom scores (nasal discharge, stuffiness, nasal itching, sneezing, and ocular symptoms) responded similarly. A smaller proportion of patients in the SCH 434 group reported side effects, especially dry mouth (7% vs 19%, P = 0.07), fatigue (6% vs 25%, P < 0.01), and sedation (7% vs 22%, P < 0.03). In conclusion, the combination of loratadine plus pseudoephedrine sulfate was equally as effective as a classic antihistamine (chlorpheniramine maleate) plus pseudoephedrine sulfate but had a lower incidence of side effects.