The surface glycoprotein CD44 is widely distributed in different tissues. In contrast to healthy tissue, tumour samples show a more complex pattern of CD44 expression, indicating a loss of splice control. Beside cell-surface expression, the measurement of soluble CD44 in serum of cancer patients could be useful in early diagnosis and assessment of disease status. We evaluated the surface expression of CD44 isoforms in 22 ovarian cancer patients by means of immunohistochemistry. Additionally, we investigated 134 serological samples of these patients for the occurrence of CD44 isoform expression. For CD44 standard, CD44v5 and CF44v6 mean serum levels in patients with clinically detectable or non-detectable ovarian cancer were 422.4 +/- 143.8 ng ml-1 and 547.4 +/- 148.2 ng ml-1, 12.3 +/- 7.9 ng ml-1 and 21.9 +/- 12.2 ng ml-1 and 105.5 +/- 37.9 ng ml-1 and 144.9 +/- 50.9 ng ml-1 respectively (P-values not significant). CD44 surface proteins containing epitopes encoded by splice variants CD44v5, CD44v6 and CD44v7-8 were immunohistochemically detected in 9% (n = 2), 13% (n = 3) and 4% (n = 1) of the 22 tumour samples respectively. In the present study we showed that in ovarian cancer CD44 isoforms CD44v5 and CD44v6 are expressed in very low amounts by the tumours. In accordance with this, we found that the presence of tumour is not associated with higher serum levels of CD44standard, CD44v5 and CD44v6 in preoperative serum samples in ovarian cancer patients.