1. The ideal drug treatment for atrial fibrillation will control resting heart rate, blunt exercise induced tachycardia whilst not exacerbating nocturnal bradycardia. Monotherapy with digoxin may not be ideal. We have compared the effect of combining digoxin (0.25 mg daily) with atenolol 50 mg and 100 mg or pindolol 5 mg twice daily and 15 mg twice daily in a cross-over randomised single-blind trial in eight symptomatic patients (six male; mean age 62 years) with poorly controlled atrial fibrillation. 2. Heart rate control was measured by 24 h ECG at baseline on digoxin therapy and after 2 weeks with each treatment. Symptom scores for breathlessness and palpitation were measured using visual analogue scales. 3. The addition of both beta-adrenoceptor blockers significantly reduced mean diurnal maximum heart rate from baseline (all P < 0.001 ANOVA). Atenolol at both doses caused a greater reduction than either dose of pindolol (P < 0.001 ANOVA). Nocturnal maximum heart rate was not significantly reduced from baseline by either beta-adrenoceptor blocker, but both doses of pindolol caused increases in nocturnal maximum heart rate compared with atenolol (P < 0.001 ANOVA). 4. Atenolol caused a reduction in diurnal minimum heart rate compared with baseline and caused a reduction in nocturnal minimum heart rate whereas pindolol caused an increase (P < 0.001 ANOVA). 5. Atenolol 100 mg caused longer nocturnal pauses compared with baseline but pindolol 15 mg twice daily reduced the number of nocturnal pauses > 1.5 s (P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)