The recovery of pulmonary function were studied in fifty patients of acute bronchial asthma receiving a standard therapeutic regime. Sixty-two per cent of patients had achieved 50% of their total improvement in peak expiratory flow rate (PEFR) within 24 hours (fast responders) as against slow responders. Duration of asthma, characteristics of present exacerbation, mean pulse rate and presence of pulsus paradoxus on admission did not differ in fast and slow responders. The rise in PEFR within 4 hours of starting treatment was highly significantly correlated with a higher PEFR at 24 hours and a faster recovery. The mean arterial PaCO2 was higher (P less than 0.02) in slow responding group and they were slightly older (P less than 0.01), had lower mean FVC (P less than 0.01), mean FEV1 (P less than 0.02) and PEFR (P less than 0.001). The mean PaO2 of less than 80 mm Hg at 48 hours was more common in those with delayed recovery of PEFR.