The aim of the study was to assess the specificity of albumin-messenger RNA (mRNA)-positive cells in peripheral blood as an indicator for circulating malignant hepatocytes. Albumin-mRNA-positive cells in the peripheral blood mononuclear cell (PMNC) fraction were detected by reverse-transcription polymerase chain reaction (RT-PCR). Albumin-mRNA-positive cells in PMNC were found in 12 of 19 (63%) patients with hepatocellular carcinoma, but also in 22 of 25 (88%) patients with chronic hepatitis without evidence for hepatoma, and in 18 of 19 (94%) of patients with acute viral hepatitis. In addition, 8 of 28 (28%) of healthy control individuals had also albumin-mRNA-positive cells in peripheral blood. PMNC known to be spontaneously negative for albumin-mRNA could be induced in vitro to transcribe albumin-mRNA after activation with a variety of substances such as interleukin-1 (IL-1) plus concanavalin A (Con A), IL-2, bacterial lipopolysaccharide, platelet derived growth factor, alpha-fibroblast growth factor, or hepatocyte growth factor. These results show that the majority of patients with acute and chronic liver disease without evidence for hepatocellular carcinoma has albumin-mRNA-positive cells in their PMNC fraction indicating the nonspecificity of that parameter for the presence of circulating malignant hepatocytes. In addition, in vitro experiments suggest that PMNC are capable of transcribing mRNA for albumin at a low level after activation. In vivo-activated PMNC are likely to be the source of positivity in healthy controls, patients with nonmalignant acute and chronic liver disease, and patients with hepatocellular carcinoma.