Oviposition of Boophilus microplus (Canestrini) was studied under varying conditions of temperature, light and humidity. Eggs were laid throughout the temperature range of 55-102°F., with the optimum temperature between 80-850F. A temperature of ro5°F. inhibited oviposition completely but was not lethal to the adult; a temperature of ro7°F. for 24 hours was lethal. Engorged ticks survived for over 90 days at a t emperature range of 40-6o°F. (mean 50°F.) but oviposition was limited and theeggsnotviable. Relative humidities of less than 30 % and immersion in water for over 24 hours severely inhibited oviposition; light had little influence on egg-laying.