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The Drosophila retinal degeneration B protein (RdgB) is a novel integral membrane phosphatidylinositol transfer protein required for photoreceptor cell viability and light response. We isolated one intragenic suppressor ([rdgB.sup.su100]) and four autosomal suppressors of the hypomorphic [rdgB.sup.KS222] retinal degeneration phenotype. The [rdgB.sup.su100] suppressor dramatically slowed [rdgB.sup.KS222]'s photoreceptor degeneration without significantly improving the electroretinogram (ERG) light response. One autosomal recessive suppressor [su(rdgB)69] significantly slowed [rdgB.sup.KS222] retinal degeneration and restored the ERG light response near to that of the wild type. Unlike all the previously characterized rdgB suppressors, the four new autosomal suppressors do not affect the ERG light response in [rdgB.sup.+], flies. Only Su(rdgB)116 exhibited a mutant phenotype in a [rdgB.sup.+] background, which was smaller R1-6 rhabdomeres. We also examined the extent to which two previously identified visual transduction mutations suppressed rdgB retinal degeneration. Absence of one of the light-activated calcium channels ([trp.sup.CM]) slowed the onset of rdgB-dependent degeneration. However, loss of protein kinase C ([inaC.sup.209]), which blocks photoreceptor cell deactivation, desensitization, and light adaptation, failed to suppress rdgB degeneration under normal light conditions. This demonstrates that TRP activity, but not INAC, is required for rapid rdgB-dependent degeneration.