Monthly trends in mortality and hospital admission rates attributed to asthma for those aged 15 to 34 for the province of Ontario were examined for the period 1979 to 1986. Graphs showing the monthly variation after the elimination of trend are presented. Time series models were constructed to evaluate the statistical significance. Asthma hospital separations peaked in the autumn and a test for seasonality was statistically significant (p less than 0.001). Although the pattern for asthma mortality was similar, the test for seasonality was not significant (p greater than 0.10).