Immune complexes have been assayed sequentially in seventeen patients with gynecological malignancies, using a polyethylene glycol precipitation assay and a Clq solid phase assay. The PEG assay demonstrated a good correlation between PEG assay levels and the course of disease in nine out of eleven patients with ovarian adenocarcinoma and all four patients with endometrial carcinoma. Three of the patients with ovarian cancer were not treated with aggressive surgery and exhibited equivocal signs of progressive disease during subsequent follow-up. There was no clear relationship between immune complex levels and the clinical condition in two of these patients. The ClqSP assay result did not correlate with disease progression and, in several instances, progressive disease was associated with a fall in ClqSP values. In a further series, twelve out of twenty patients with ovarian cancer who were initially in remission from disease but subsequently relapsed demonstrated elevated levels of PEG immune complexes between one and three months before clinical detection of recurrence whereas patients who stayed in remission maintained normal levels of PEG immune complexes. These data suggest that the PEG assay may be of clinical value in the monitoring of ovarian cancer patients with minimal residual disease following surgery.