Response curves for the abundance value of chironomid species against water temperature were analyzed and optimum, tolerance, skewness and kurtosis calculated. The data base consisted of 127 taxa and 991 sites in running waters in Italy. Optimum temperature was calculated as weighted mean temperature, tolerance as weighted standard deviation, skewness and kurtosis as 3rd and 4th moment statistics respectively. Species were sorted according to optimum temperature. Most species are cold stenothermal and show tolerance for a narrow temperature range, very few species have a clearly plurimodal response. Cold stenothermal species have an optimum near their minimum tolerance value, warm water species have an optimum near their maximum tolerance value. The warm water species are more or less eurythermal. Lack of data prevents the demonstration of a relationship between thermal tolerance and the position of a species in the evolutionary tree, but the problem is worthy of further study.