Abstract: The incorporation ire vivo of 35S-methionine, 3H-uridine and 32P-NaH2PO4 by the third-stage infective larvae in A, sinensis was investigated respectively by means of membranous feeding. The quantity of the three radioisotopes in these larvae were not equal. For example when 35S-methionine and 32P-NaH2PO4 were given to mosquitoes in almost equal quantity, the radioactivity was higher for the former than the latter in both the mosquitoes and larvae. The present study has provided an in vivo method for studying the biology of B. malayi larvae under the natural condition.