Elevated amounts of cell-free nucleic acids are detected in the circulation of cancer patients. The type and pattern of these may vary depending on the origin. Recently, we described the presence of circulating fragmented nucleosomal DNA. In the present study, our aim was to investigate the association between nucleosomal DNA, caspase-3 expression and circulating caspase-3 mRNA, the primary activator of nucleosomal DNA fragmentation. DNA fragmentation was analyzed by gel electrophoresis, and caspase-3 was analyzed by RT-PCR. Plasma samples from 65% of patients were positive for nucleosomal DNA fragmentation, whereas none of the healthy controls showed DNA fragmentation (P = 0.0004). Expression of caspase-3 differed significantly between the cases and controls (P < 0.0001). However, we observed no direct correlation between nucleosomal DNA fragmentation and caspase-3 expression in lymphocytes (P = 0.145). Circulating plasma caspase-3 mRNA was detected by nested RT-PCR, and no significant difference was observed between the patients and the control group (P = 0.5). Our results indicate that caspase-3 expression is increased in lymphocytes from patients. When compared to healthy individuals, no differences were observed in the amount of circulating mRNA. These findings suggest that nucleosomal DNA fragmentation is not correlated with elevated levels of apoptosis and circulating caspase-3 mRNA in circulating tumor cells. (c) 2005 Elsevier Inc. All rights reserved.