The antihypertensive effect of a fixed dosage combination of the cardioselective beta-adrenoceptor blocker, atenolol, and the oral thiazide-like diuretic, chlorthalidone (Tenoretic) was studied in 24 hypertensive Nigerians in a double-blind, cross-over comparison with three other treatments. These were atenolol alone, 100 mg daily, chlorthalidone alone, 25 mg daily, and atenolol (100 mg) plus chlorthalidone (25 mg) daily taken as separate formulations. Tenoretic was taken as a once-daily tablet containing 100 mg atenolol plus 25 mg chlorthalidone. The order of administration of the drugs was randomized. Each drug was taken for 4 weeks. The results showed that atenolol and chlorthalidone lowered blood pressure to the same extent. Combination of the two drugs whether taken separately or in fixed-dosage combination was better than either product singly. The drugs were well tolerated.