In recent years, the public has become more aware that exposure of males to certain agents can adversely affect their offspring; for example, fathers who smoke appear to give rise to tumours in the F1 generation (Sorahan et al., 1997a and Sorahan et al., 1997b; Ji et al., 1997). ( 1994) has reported an increased incidence of miscarriages after potential exposure to a variety of agents. Also, (1998) have shown that the paternally transmitted and paternally imprinted gene, MEST, is involved in normal maternal behaviour. MESTdeficient females show abnormal behaviour and intrauterine and postnatal growth retardation of progeny. This is even more evidence of how important the male is to the successful development of the future generation.