Andervont (2) has recently reviewed the litera ture on the occurrence of spontaneous hepatomas in C8H and CBA mice. It is now well established (1, 3, 6, 10, 13, 14) that mice of these strains may develop spontaneous hepatomas and that these tumors most commonly arise in older mice, i.e., those more than 1 year old. Furthermore, many previous studies (2, 4-7, 9, 10) on C3H and CBA mice have indicated that spontaneous hepatomas occur more often in males than in females; con versely, Andervont (2) has reported that there was a lower incidence of these tumors in castrated C3H males than in intact litter-mates. The relationship between hormonal stimulation and the development of spontaneous hepatomas in mice has also received attention. Shimkin and Wyman (12) decreased the incidence of spontane ous hepatomas in C3H males by giving estrogen. However, Burns and Schenken (4) and Schenken and Burns (11) found that estrogens increased the incidence of these tumors in C3H males and de creased the incidence in C3H females; and, of 48 C3H males and females treated with testosterone propionate, only one female developed a hepatoma. Again, although Miller and Pybus (8) de creased the incidence of hepatomas in castrate CBA males by giving estrogen, they also reported (10) that there was no diminution in the incidence of hepatomas in intact CBA males injected with estrone. Thus, as Andervont (2) has pointed out, "It is clear, as indicated by all these investigators, that further efforts along these lines are essential."