We analysed antibodies to Epstein-Barr virus nuclear antigens (EBNAs 1, 2, 5 and 6) and the presence of serum p53 in 100 individuals, 37 of whom has developed a haemopoietic malignancy during a 12-year follow-up of 39,000 Finnish adults. Serum p53 was detectable in six of the 63 (10%) matched controls and in 13/31 (42%) patients who developed a malignancy of lymphoid origin approximately 7 years after serum withdrawal. Six patients who developed a malignancy of myeloid origin were negative for p53. The presence of p53 alone was associated with a highly significant increased risk of lymphoid malignancies (relative risk (RR)p53 = 6.7, 95% confidence limits (CL) 1.9, 24) whereas high levels of antibody to EBNA2 seemed to be inversely related to the risk (RREBNA2 = 0.1, CL 0.0, 1.1). Among lymphoid malignancies, a combination of serum p53 and high EBNA1 antibody levels gave a greater than expected risk (RRp53 and EBNA1 = 14, CL 1.4, 130; RRexpected = 4.4), whereas interaction with high levels of EBNA5 antibody gave an expected risk (RRp53 and EBNA5 = 19, CL 1.7, 220; RRexpected = 17). Thus detectable levels of p53 appear early in the development of lymphoid malignancies, and high EBNA1 antibody levels, and accumulated p53 may both be synergistic risk indicators for lymphoid malignancies, whereas high EBNA5 antibody levels and accumulation of p53 seem to raise the RR independently of each other.