A multiple regression analysis was performed of factors affecting the prognosis of 93 patients with metastatic malignant teratoma treated at the Royal Marsden Hospital between 1979 and 1981. In a subgroup of 53 patients, where exact tumour bulk could be calculated from sequential CT scan slices, a correlation was seen between tumour marker level and volume of metastatic disease. On analysis of the risk of relapse after initial chemotherapy, the independent adverse influence was detected of serum AFP greater than 500 micrograms/l and of bulky disease defined by clinical staging. An adverse influence of high serum HCG levels was not seen, probably due to the small number of patients in this series with this presenting feature.