Ten patients with moderate heart failure who still had symptoms despite 40 mg frusemide daily were treated with increased doses of frusemide and the addition of captopril in randomised order. Four different methods were used to assess the patients' response to treatment. Both treatments improved symptom-limited exercise tolerance, higher-dose frusemide having a more favourable effect. Perceived exertion during submaximal exercise was reduced by similar amounts by both treatments. The time taken to walk 100 m at a self-selected slow speed was reduced by both treatments; again higher-dose frusemide had a more beneficial effect. The higher dose of frusemide also had a more favourable effect on visual analogue scores for dyspnoea, fatigue, and general well-being.