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Several points have been raised about homocysteine stabilisation and measurement - and the two problems are very much inter- related. In addition to the problems of practicability (138 mins elution time per injection, as Graham Icke points out) I don't believe that amino- acid analyser techniques (developed for urinary analysis, originally qualitative and designed to detect high levels) can reliably quantitate Hcys at the levels we are now looking for in plasma. In reply to Frank Konstantinides, I haven't got the literature in front of me as I write, but I think we are talking about the work of one group in particular, about 10 years ago. It's a question of whether the peak will actually be there when it gets to the detector, Prof Frank ! One of the reasons for the current confusions is that previously published results are often based on inappropriately collected specimens, using methods that destroy Hcys during the analytical process. IMx sounds like a good method, although I haven't tried it. The literature by and large recomends EDTA plasma from anti- coagulated blood as the best specimen. Once the plasma is frozen the Hcys content has been shown to be stable for many years, until you unfreeze it. The concentration of EDTA in BDH Venoject tubes is 1.5 mg/ml (once the tube is full of blood). If you add sodium fluoride to give a final concentration of 5.0 mg/ml, the Hcys is effectively stabilised to enable the whole blood to get through the specimen transport and separation procedure (even postal delivery) before separation. If you take blood into EDTA alone, a decline in Hcys can be detected within two hours, so the specimen must be separated and frozen PDQ. Somewhat peversely I haven't tried the tubes that BDH actually produces for such situations (BDH potassium oxalate with added sodium fluoride - 366427-7R0003) since they make them in a very small size which only yields about 1.0 ml of plasma ! They are probably suitable, but perhaps someone else would like to try them out ? Best wishes, Nick Miller, London %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%