This paper presents some results of field and laboratory studies on Bulinus truncatus, the snail intermediate host of urinary bilharziasis in Iraq, made in 1958 as part of the work of the WHO Bilharziasis Control Project in that country.Observations on the linear distribution and size composition of Bulinus populations in the canals of central Iraq indicate that molluscicides might most suitably be applied in May before the entire snail population reaches breeding size, or early in November when most snails are juveniles. However, laboratory experiments appear to show that isolation of individual bulinid snails does not diminish, but may actually increase, their egg-laying capacity in comparison with that of grouped snails; this suggests that, even if the snail population were drastically reduced by treatment of the canals and all further importation of snails rendered impossible, the snail population would nevertheless soon renew itself from the few individuals remaining.Results are also given of laboratory experiments on egg masses, hatching and growth of B. truncatus and on the egg-laying of random populations of that snail.