The Becton-Dickinson VACUTAINER BRAND SERUM SEPARATOR TUBE (SST) was evaluated in a field test in five hospitals. The SST evacuated blood drawing tube contains a semi-solid silicon polymer which migrates to the serum-clot interface during centrifugation causing a barrier to form which separates serum from red cells. Eighteen clinical chemistry determinations were studied. No clinically significant SST induced changes were observed when compared to conventional blood drawing tubes. Statistically significant changes (t-test, p=0.05) were observed for bicarbonate, calcium, chloride, cholesterol, glucose (Beckman Analyzer), and sodium. For each test (glucose, uric acid, etc.) data were analyzed twice; once as a complete set, and once as a subset consisting of abnormal data only. The small, statistically significant LDH bias observed in the earlier (2,3) clinical trials was not present.