UV irradiated spores of Streptomyces sp. AP 19-1 strain that can produce antibiotics were incubated at 27 degrees C, and 33 degrees C which is close to inhibiting growth temperature, respectively. The results showed that there were much more forward mutants, whose level of producing antibiotics is higher than that of original strain, among the offspring of UV irradiated spores grown at 33 degrees C, compared to that grown at 27 degrees C. The percentage of the forward mutants was 25.8 % at 27 degrees C and 58.1% at 33 degrees C. The progeny strains and the original strain were tested by RAPD using total DNA with 17 primers. It was demonstrated that more variations occurred in the chromosomal DNA of the progeny strains grown at 33 degrees C than in that at 27 degrees C. This method facilitates increasing the efficiency of induced mutagenesis in breeding and provides a new way to study the mechanisms of mutation formation in UV irradiated Streptomyces sp. cells.