To examine the molecular basis of efficient superovulation in the Mastomys (Praomys coucha), the cDNA sequences of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) β-subunits were determined and compared with those of other mammals. FSHβ and LHβ cDNAs were 1606 and 513bp long, respectively, from the 5′-ends to the putative polyA sites. The deduced sequences of the FSHβ and LHβ precursor proteins were 130 and 141 amino acids in length, respectively. The amino acid sequences of both mastomys hormone subunits showed overall similarity to those of other rodents. In particular, the N-terminus of the FSHβ precursor protein is of the MM-type, like those of mice and rats, which suggests that the MM-type is characteristic of the subfamily Murinae. As we reported earlier for the Mongolian gerbil, the use of hCG for superovulation of mastomys might need to be re-evaluated, due to the low homology between hCG and rodent LH sequences.