3,4-methylenedioxymethamphetamine (MDMA) is a psychotropic substance with both stimulant and hallucinogenic properties. MDMA is chemically related to other designer drugs such as 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxyethylamphetamine (MDEA). A rapid method of blood analysis by means of liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization (LC-MS/APCI) has been proposed for detection and quantitation of methylenedioxymethamphetamines. The proposed methodology requires 0.2 ml of blood or serum. Established limits of detection for all analytes were below 1 ng/ml. Limits of quantitation were 5 ng/ml. A statistical evaluation of obtained positive results is presented. Almost 10% of positive MDMA cases were classified as drug-facilitated sexual assaults (DFSA). Half of the determined concentration of MDMA was within the range of 80-200 ng/ml. Some practical remarks on blood analysis for MDMA are made.