The matrix metalloproteinases MMP-7 and MMP-11 (with MMP-11 being more specific and reliable) proved to be specific and reliable markers for the differentiation between menstrual blood and blood due to trauma. This study attempted to establish a real time-PCR-based assay for the detection methods for menstrual blood, and to provide data for a better differentiation between true positive and negative results, using quantitative real time RT-PCR. Results showed that MMP-7 could be detected in 54 of 60 menstrual blood samples, and was never detected in any of the control blood samples and in the vaginal and semen samples when the cycle number did not exceed 40. The identification of body fluids can be of crucial importance in forensic casework. Recently, the detection of cell- and tissue-specific mRNAs was found to be a suitable technique to identify menstrual blood and semen. However, the new technique provides quantitative results thus allowing a cut-off value for the control marker GAPDH to be defined, below which negative results for the menstrual blood marker MMP-7 allow the conclusion that the sample was not menstrual blood. Case examples are provided which show that the correct identification of samples as non-menstrual is likely to be in the focus of criminal investigations; recent case experiences have shown that the forensically most relevant substrate is menstrual blood. Figures, references