Ambient air lead concentrations have been measured in Helsinki since 1978. The mean concentrations at various stations reached maximum values in 1980, being then 209-1150 ng/m3. From 1980 to 1991 the concentrations decreased to one-eighth (335-41 ng/m3) at the three stations where measurements were made continuously. Concomitantly the estimated annual lead emissions in Helsinki decreased from 78 to 9 tons, mainly owing to the reduced emissions of lead in exhaust gases from road traffic. The mean concentration of lead in the blood of children in day-care centres was 46 micrograms/l in 1983 and 30 micrograms/l 5 years later. Similar concentrations were found in blood samples from a day-care centre beside a street with heavy traffic and in those from an area with less traffic.