For the determination of homocysteine, the sample is reduced and derivatized in one step. The albumin bound and the oxidized homocysteine is reduced and converted into a fluorescent probe. During a precipitation step high molecular substances are removed. The sample is cooled at 2-8°C, centrifuged and injected into the HPLC system. The isocratic separation via HPLC at 30°C uses a ``reversed phase'' column. One run lasts 5 minutes. The chromatograms are recorded by a fluorescence detector. The quantification is performed by the delivered plasma calibrator; the concentration is calculated via the ``internal standard method'' by integration of the peak areas resp. peak heights. Sample Types: serum, plasma. Time: 10 minutes ? Homocysteine is an amino acid, which is produced out of methionine. It is not ingested by nutrition. Homocysteine is rapidly degraded to cysteine when vitamin B6, folic acid and vitamin B12 are sufficiently available. Increased levels of homocysteine will damage heart and blood vessels. Meanwhile it is an established risk marker for cardiovascular disease. US studies demonstrate that 40% of heart attacks are caused by increased homocysteine levels. Also the risk for stroke is increased by elevated homocysteine concentrations in plasma. A participation of homocysteine in Alzheimer and Parkinson diseases are under discussion.