The aim of this study was to assess a possible relationship between the concentration of total suspended particles (TSP) and aggravation of symptoms in patients with chronic obstructive pulmonary disease (COPD) with regard to the trend, seasonality and weather conditions. Data on the number of COPD patients reporting aggravated symptoms, mean TSP concentrations, temperature, air pressure, and relative humidity were collected daily for years 1994 and 1995 in Zagreb, Croatia. The authors found a statistically significant correlation between the number of aggravated COPD cases and the TSP concentrations on the previous day. There was a significant autocorrelation in residuals with a lag of 8 days. The estimated value of the regression coefficient for the concentration of TSP on the previous day was 0.001692 (s.e. = 0.000797, p = 0.0345). The estimated relative risk, corresponding to a change of 10 micrograms/m3 in the mean daily concentration of suspended particles, was 1.184 (95% confidence interval: 1.013-1.385).