Polycystic kidney disease (PKD) is a prevalent inherited disease in human beings. The pathogenesis of PKD is as yet unclear. The epidermal growth factor family of proteins has been implicated in PKD based largely on in vitro data. To determine whether these growth factors contribute to the progression of inherited PKD in vivo, we crossed mice with a transgene for human transforming growth factor-alpha (TGF-alpha, a member of the epidermal growth factor (EGF) family) and mice with the pcy gene (which causes a slowly progressive form of PKD very similar to human autosomal dominant PKD). Renal expression of the TGF-alpha transgene in cystic mice (homozygous for the pcy gene) accelerated the development of PKD as shown by an increased kidney weight as a percent of body weight and an increased volume density of renal cysts at 8.5 weeks of age. However, renal expression of the TGF-alpha transgene did not appear to precociously initiate cyst development (at 6.5 weeks), nor did it cause an increase in the final degree of renal enlargement (at 29 weeks). Thus TGF-alpha accelerated the enlargement of cysts once initiated. At 8.5 weeks of age, renal expression of the TGF-alpha mRNA correlated positively with the amount of renal enlargement. At all time points studied, cystic kidneys exhibited increased expression of c-myc mRNA as compared with phenotypic normal kidneys, consistent with PKD being a hyperplastic disease of renal tubules. However, the renal expression of c-myc in 8.5 week cystic kidneys, with or without the transgene, did not correlate with the degree of renal enlargement. The results of this study suggest that EGF-like proteins may accelerate the progression of inherited renal cystic disease. However, the final degree of cystic change is dictated by the primary disease process rather than by the continued presence of growth factor.