The beta subunit of human chorionic gonadotrophin (beta-hCG) and Schwangerschaftsprotein 1 (SP1) were measured by radioimmunoassay in the serum and cerebrospinal fluid (CSF) of 46 postmolar and postpartum patients who developed gestational trophoblastic disease. There was a significant correlation between beta-hCG and SP1 serum levels. The mean serum SP1 level in high-risk patients was significantly higher than that in low-risk patients. There was a significant correlation between serum and CSF beta-hCG levels. The ratio of serum to CSF beta-hCG levels was low in the three patients with clinical evidence of intracranial metastasis. SP1 was present in the CSF of only one of these three patients, but it could be detected in the CSF of another four patients without clinical evidence of metastases in the central nervous system. The two low-risk patients with SP1 present in the CSF showed poor response to intramuscular methotrexate.