Phosphatidylinositol 4,5-bisphosphate phosphodiesterase activity was found to be almost absent in the compound eyes of Drosophila visual mutant, norpA (no receptor potentials A). We compared the enzyme activities among independently isolated norpA alleles, each having a different degree of the vision defect. A close correlation was found between the size of receptor potentials (electroretinogram), phototactic behavior and the enzyme activity. The correlation exists not only among alleles, but also in a single, temperature-dependent allele under different temperature; the enzyme activity of flies kept at 18 degrees C (phototactic) was about five times higher than that of the ones kept at 28 degrees C (blind). These results suggest that hydrolysis of phosphatidylinositol 4,5-bisphosphate is involved in phototransduction process in Drosophila eyes.