A double-blind crossover study was performed to evaluate the bronchodilating effect of different single doses of procaterol (less than 0.5 micrograms/kg, 1.5 micrograms/kg, and placebo) orally administered. Sixteen asthmatic children, age 6-12 years, participated in the trial. Pulmonary function, heart rate, blood pressure, and tremor were evaluated at 30, 60, 90, and 120 min and then hourly for 8 hours after administration. All three doses were therapeutically effective. The 1.5 micrograms/kg dose produced a more sustained bronchodilatation effect, but was also associated with an increase in the incidence of tremors. The 0.5 micrograms/kg dosage may, however, be a good starting dose because it assures a reasonable risk/benefit ratio.