Auxotrophic, spore color, and alkaloid biosynthetic mutants of Penicillium roquefortii were selected after N-methyl-N'-nitro-N-nitrosoguanidine treatment. Diploids were obtained via protoplast fusion techniques, and the segregants from a diploid were genetically analyzed. The data demonstrated the potential of parasexual recombination in this organism. Evidence was obtained which suggests that the his and sts (sensitivity to Sulfatase) genes may be linked. The genetic information obtained in this study can serve as a starting point for further mapping of genes in P. roquefortii, and indications are that this organism may serve as a promising vehicle for the genetic study of the formation of ergoline alkaloids.