In several types of solid tumours, circulating antibodies to p53 are seen in about a third of cases with a p53 mutation, but are absent in cases without p53 mutation. Therefore detection of those antibodies has relatively low sensitivity but high specificity in the detection of p53 mutations. We looked for circulating p53 antibodies by ELISA in 56 adult non-Hodgkin's lymphoma (NHL) and 80 multiple myeloma cases. A certain or highly probable p53 mutation was found by SSCP analysis, immunocyto- or immunohistochemistry in 8/35 (23%) NHL cases and 2/19 (10%) MM cases analysed by these techniques. None of the 80 MM cases and only one of the 56 cases of NHL had circulating p53 antibodies. The positive case had Burkitt's lymphoma and a p53 missense mutation at codon 273. Thus, very few MM and NHL patients with a p53 mutation develop p53 antibodies and this test does not appear to be useful in haematological malignancies.