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The discovery of two stable male-sterile genes and the prevalence of adequate insect-aided cross-pollination led to the development and release of the first pigeonpea [Cajanus cajan (L.) Millsp.] hybrid in India. Commercialization of this hybrid is constrained because of the labor intensiveness of seed production and concerns about seed purity. Cytoplasmic male-steriles would effectively circumvent these constraints and revolutionize the hybrid seed industry. This paper reports the development of cytoplasmically determined male-sterility, which was accomplished by two methods: wide hybridization involving conventional backcrossing of Cajanus sericeus van der Maesen and Cajanus cajan and multiple cross genome transfer. In these matings, two forms of reversion to fertility were noticed, one influenced by low temperature and high humidity, and the other probably determined by genetic factors alone. The influence of temperature on fertility restoration as reported for Viciafaba L. is different from that seen in species crosses of Cajanus. The multiple cross genome transfer method resulted in stable cytoplasmic-genic male sterility maintainable by the pigeonpea genotypes ICPL 85030 and ICPL 90035. These male-sterile lines are in agronomically desirable backgrounds. P IGEONPEA is unique among cultivated plants for the diversity of its mating systems, which arises from heritable alterations of the floral structures, initially adapted to self pollination. Mechanisms of partial outbreeding evolved over time and it is the norm for the species. Subsequent modification of the staminal structure from diadelphous to filamentous form led to a stable self-pollinating mechanism (Saxena et al., 1992) and the evolution of male-sterility led to complete out-breeding (Reddy et al., 1978; Wallis et al., 1980). These mating systems impart distinctly different genetic structures to populations, each having its specific use. All three sys