The non-Mendelian genetic element of a given mating type of Chlamydomonas reinhardtii was first doubly marked by succesive mutageneses and then transferred into a number of offspring cells of the opposite mating type. In subsequent crosses of these offspring clones, the transmission pattern of the original non-Mendelian markers was analyzed. The results indicate that the mating-type gene of a given cell regulates the transmission and perhaps the recombination of the non-Mendelian genes regardless of whether the non-Mendelian markers were isolated originally in the same cell or obtained from another cell of the opposite mating type through genetic transmission. The regulation of the transmission of non-Mendelian genes in C. reinhardtii is thus apparently different from the autonomous control of the transmission of non-Mendelian mitochondrial genes in yeast by a genetic factor located on the mitochondrial genome.