Eight experimental populations of Drosophila buzzatii were founded with adults derived from the locality of Arroyo Escobar (Argentina). The populations were fed on different trophic substrates for more than 30 generations and periodically a sample of individuals from each of them was studied for chromosomal polymorphism. Considerable changes in the frequencies of second chromosome arrangements occurred in the eight experimental populations and the response varied significantly according to the different treatments. These results show the remarkable influence the trophic substrate has on second-chromosome polymorphism of D. buzzatii. © 1985 Dr W. Junk Publishers.