We have used immunoprecipitation to test tumor biopsies and normal adult and fetal human tissues for p97, a tumor-associated protein. Five of nine melanoma biopsies contained p97 in low to very high levels. Three of seven non-melanoma tumors contained p97, but in smaller amounts. No p97 was detected in any of the normal adult tissues examined. The protein was, however, observed in samples of fetal colon and umbilical cord, and in one sample of fetal lung. One of two benign nevi contained high levels of p97, whole on benign angiofibroma was negative. We conclude that the presence of p97, in levels detectable by our method, appears to be characteristic of certain neoplastic and fetal tissues.