Four geographically distinct colonies of the human head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae) were reared on a live host and exhibited significantly different life history patterns. Florida head lice exhibited approximately 10% slower development and approximately 15% reduced longevity relative to California or Ecuador head lice. Fecundity (4.9 +/- 0.2 eggs/female/d) and fertility (76.4 +/- 2.9% mean hatching rate) declined over the lifetime of female lice, especially when separated from males (i.e., unmated recently). All four colonies (above plus one from Panama) were similar in their ability to tolerate starvation, although older stages tended to die sooner. An in vitro feeding apparatus was developed to rear head lice. Teneral first instar lice were placed on human hair tufts on the upper side of membrane-covered feeders, which were immersed bottom-side down within a vessel containing warmed human blood. Relative to lice reared on a human host, in vitro-reared lice required a significantly longer time (10-20%) to molt and survived a significantly shorter time as adults (30-50%); the addition of antibiotics did not adversely affect louse development. Teneral first instars were more likely than any other stage to feed through the membrane. Lice spent a significantly greater proportion of time searching in the in vitro apparatus than on a host, but the proportion of time spent feeding did not differ. This research is the first to demonstrate that head lice can be reared successfully in vitro through a complete life cycle.