The results of experiments to explore the possible existence of a heat shock locus in Chironomus and Anopheles which may be comparable to the 93D heat shock locus of Drosophila, are presented. None of the heat shock loci in C. striatipennis were inducible by benzamide, colchicine, vitamin B6, thiamphenicol or a homogenate of heat shocked glands, all of which are known to selectively induce the 93D-like loci in the genus Drosophila. Benzamide also failed to induce any locus in A. stephensi. The effect of all these treatments on general transcription in Chironomus and Anopheles polytene nuclei were comparable to those known in polytene cells of Drosophila. It thus appears that a heat shock locus homologous to 93D of D. melanogaster is absent in Chironomus and Anopheles so far as inducibility of a puff by specific agents is concerned. The existence of a possible 'functional counterpart' of the 93D locus in Chironomus and Anopheles genomes cannot be eliminated.