The susceptibility of hosts to filarial infection during pregnancy and lactation was studied using Dipetalonema viteae in Mastomys natalensis as working model. Though no difference in prepatency could be observed yet significantly higher density of microfilaraemia than controls was detected in both pregnant and lactating groups. Extended duration of patency was also found in both pregnant and lactating animals. On autopsy, animals exposed at the time of pregnancy or lactation revealed significantly higher recovery of adult worms as compared to normal controls. Thus pregnancy and/or lactation may lead to higher density and duration of microfilaraemia and enhanced establishment of adult worms in female mastomys which are otherwise less susceptible to filarial infection.