The performance of Anabaena-free (algae free) and symbiotic types of three speeies of Azolla ( A. filiculoides, A. pinnata and A. microphylla ) were studied in a phytotron at two average temperatures (22 and 33 o C). The growth of both the Anabaena-free and symbiotic types were depressed at a high temperature (33 DC) to varying degrees for all species of Azolla tested. There was a marked reduction of both growth and nitrogen-fixing ability (pereent N) of the symbiotie Azalia compared to its Anabaena-free counterpart suggesting that the low tolerance of A . jiliculoides No.1 0 I to high temperature was probably dictated by the symbiont Anabaena azollae . A. azollae of both A, microphylla No. 418 and A, pinnata No.2 appeared more tolerant to high temperature than that of A. filiculaides No. 101.