A detailed analysis has been made of S genotypes in progenies derived from induced and spontaneous inbreeding processes in a clonal population of Lycopersicum peruvianum Mill. The results indicate that, in certain genetic backgrounds, induced inbreeding leads to the generation of a new S allele which usually first appears in the pistil of individuals otherwise homozygous for one of the parental specificities. When the change in specificity occurs in S heterozygotes, spontaneous self-compatibility is promoted and the new allele can be transmitted, via selfing, to the following generation.The factors and mechanisms which may be involved in the generation of new specificities at the S locus of higher plants are discussed and preliminary evidence is provided which suggests that the hypothesis of mutation by equal crossing-over is not applicable to the present study.