The objective of this study was to evaluate the efficacy of an Asthma Nurse Practice (ANP) in primary health care. A 12-month (September 1994-August 1995) open, prospective intervention study with pre- and post-test comparisons was performed on patients with asthma treated at a primary care centre in Sweden. Sixty-three patients with mild or moderate asthma participated and medication, structured follow-up and education in self-management at an ANP were assessed over a 12-month period. The main outcome measures assessed were pulmonary function, eosinophil cationic protein (ECP) in serum, respiratory symptoms, patient knowledge of asthma and emergency visits. ANP in primary health care increased patient knowledge of asthma and medication. The number of patients with nocturnal symptoms decreased significantly. Pulmonary function was improved: vital capacity (VC) 98-106, forced expiratory volume in 1 sec (FEV1) 93-100 and peak expiratory flow (PEF) 98-115% of predicted (P < 0.001). Variation in PEF fell from 21 to 12% (P < 0.001). ECP was significantly reduced. Visits to the emergency room were 60% fewer during the year of intervention (P < 0.01). In conclusion, patients attending an Asthma Nurse Practice, comprising a structured programme for asthma management, improve their knowledge and asthma control.