We measured survivin mRNA expression in breast cancers using a fluorogenically detected reverse transcription-polymerase chain reaction, seeking relationships between expression and clinical and histological variables. The mean relative expression of survivin mRNA was 0.347+/-0.466 in breast cancers and 0.017+/-0.023 in noncancerous breast tissue resected with the tumors. A cut-off value for positivity was set at the mean + SD for expression in the noncancerous tissues; positivity for survivin mRNA expression was 90.2% (37 out of 41 cases) in breast cancers and 23% (3 out of 13) in adjacent noncancerous breast tissues. Expression in tumors varied independently of clinicopathological factors except for lymphatic invasion. As measured by our sensitive detection system, survivin mRNA is a useful diagnostic marker for breast cancer.