A study of 16 natural populations of Drosophila melanogaster from Eastern Europe, the Caucasus and Central Asia has revealed a cline in wing length associated with geographical position of the populations. Wing length was shown to be positively correlated with temperature. The coefficient of variation in wing length was significantly different in town and orchard populations. The existence of a cline in wing length in the northern part of the species range and in the region where migration must be substantial suggests strong selection pressure acting in natural populations of D. melanogaster.