An investigation was made into some lesser known aspects of the biology of the stable fly, Stomoxys calcitrans, in order to find a basis for possible means of natural control of the pest on dairy farms. The reaction of adults to different kinds of blood was tested. Diets investigated were bovine blood alternated with ovine blood, bovine blood alternated with pig's blood, bovine blood alternated with manure filtrate, bovine blood alone, ovine blood alone, pig's blood alone and manure filtrate alone. Adults could not servive on manure filtrate alone. Flies in the other treatments exhibited no marked differences as regards duration of pre-mating-, pre-oviposition- and oviposition periods. There were, however, differences in the number of eggs laid. Females maintained on bovine blood alone produced most eggs i.e. 2,3 times as many as those laid by females fed on pig's blood alone. The latter were the poorest producers. Viability and incubation period of eggs did not appear to be affected by the kind of blood fed to the adults. Flies, however, lived longer when supplied with bovine blood and died sooner when maintained on pig's blood.