This report describes a detailed behavioral study of four shi alleles, shits1, shits2, shits4, and shiST139, and their heteroallelic combinations. Flies of different heteroallelic combinations (shi/shi) were less sensitive to high temperature than the corresponding homozygotes. Among them, shits2/shits4 showed a striking reduction in temperature sensitivity. In contrast, different shi/+ heterozygotes were more severe in temperature sensitivity than the hemizygotes, Df/+. The hemizygous combinations of shi alleles over deficiency (shi/Df) were not completely lethal, with shits2 conferring distinctively higher and shits4 lower viability. A novel behavior, bang sensitivity, was also found in shi/Df. The results of allelic interactions suggest that the shi mutations examined appear to be antimorphic and that the shi gene products are likely to function in multimeric form.