We analysed peripheral blood samples from 143 patients with primary melanoma (PM) for the presence of tyrosinase mRNA by reverse transcription-polymerase chain reaction (PCR) to determine whether the early detection of circulating melanoma cells (CMCs) is of clinical value in monitoring melanoma progression. Ten of the patients (7%) with PM had detectable CMCs. The percentage of PCR-positive patients was higher for stage II patients (9.0%) than for stage I (5.3%), but the difference was not significant. A significantly higher percentage (P<0.05) of PCR-positive patients were found to have tumours greater than 1.5 mm in thickness or had ulcerated tumours. This suggests that tumour thickness and ulceration are the two most significant prognostic factors. The detection rate of 9% for patients with stage II disease is much lower than would be expected, since 23.9% (16 out of 67) of the stage II patients subsequently developed metastases. Of these 16 patients, only one was PCR-positive, 1 week before the metastases became clinically evident. Thus, the current technique fails to predict the likelihood of developing metastatic disease (P=0.3485). The other nine PCR-positive patients had not developed metastases after a median follow-up period of 4 years. It is concluded that this technique for the detection of CMCs is of limited clinical value in predicting the likelihood of metastasis in patients with PM. It is suggested that the detection of micrometastases in other anatomical compartments, such as sentinel lymph nodes, should be explored for the identification of patients at risk for developing metastases.