Cultivated alfalfa (Medicago sativa L.) is a polysomic polyploid with tetrasomic inheritance. In this crop the hybridization of gametes with the somatic chromosome number (2n gametes) produced by diploid hybrids is a valuable method to maximize heterozygosity. For this purpose it is necessary to obtain diploids which produce high frequencies of 2n gametes. The results of the present paper indicate that phenotypic recurrent selection was efficient in increasing the production of male and female 2n gametes in diploid alfalfa. Two distinct selections were carried out, one for 2n pollen and the other for 2n egg production and two cycles of phenotypic recurrent selection were performed. The percentage of plants producing 2n gametes and the frequency of 2n gametes per plant were improved by selection. Realized heritabilities over the two cycles of recurrent selection were 39% and 60% for 2n pollen and 2n egg production, respectively; on the whole, the responses to the selection indicate that both male and female 2n gamete production are controlled by major and minor genes.