The effect of age on the success of the forced mating technique was studied in Anopheles farauti No. 1. Success of this technique appeared to be independent of age within the range 11/2 to 41/2 days old. Over all only 56.4% of 1099 females which had copulated with males during this experiment were inseminated. In An. gambiae, An. arabiensis and An. farauti No. 1 is was found that when males were cooled for 24 hrs prior to being used for the forced mating technique, the number of inseminations per 100 males was increased compared with the number of inseminations per 100 males of the same species which kept under normal laboratory conditions. In all 3 species there were low rates of inseminations per 100 copulations using both the cooled and control males (45.8% to 67.3%).