The duration of immature life stages and the preoviposition period of Solenopotes capillatus Enderlein (Anoplura: Linognathidae) were determined by daily observation in vivo of individual specimens. The duration of the egg and nymphal stages was obtained by daily observation of eggs deposited by females transferred to normal predilection sites of uninfested cattle. The preoviposition period was determined by transferring third instars to uninfested cattle and then recording the period from adult eclosion to first oviposition. The egg stage required 11–13 d. Both first and second instars required 3–4 d, and third instars, based on observations of females, required 5–6 d. The preoviposition period was 2 d. Between 27 and 29 d was required for completion of the cycle (egg to egg). The size (length) of unmounted specimens, in millimeters, was egg 0.70; first instar 0.69; second instar, 0.82; third instar, 1.06; adult female, 1.50; and adult male, 1.08.