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I agree with John Kane that the problem may be due to presence of cross-reacting 3b-hydrosteroid conjugates. If this is the case it is difficult to see how it could be overcome without solvent extraction. In this respect it may be of interest to bring to your attention an extreme example of assay interference. Testosterone results are 4-fold higher by direct measurement during the first few months of life, an age when steroid conjgates abound ( see Fuqua JS et al Clin Chem 41, 1146 - 1149, 1995). These authors advise that direct methods are NOT SUITABLE for measuring testosterone in infants younger than 2 months. Dr.A.M. Wallace. PhD, MSc, FRCPath. University Department of Pathological Biochemistry Macewen Building Glasgow Royal Infirmary University NHS Trust Glasgow G4 0SF Scotland, UK Phone: +44 (0)141 211 4490 (direct) Fax: +44 (0)141 553 1703 Email: [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%