In the determination of nickel and chromium in serum, contamination is the most important source of error. In this study the influence of needle type and collection device was investigated. For each of 20 subjects the concentrations of nickel and chromium in serum obtained by the following techniques of blood collection were compared: closed collection system (acidwashed polyethylene syringes) + (A) steel needle (Terumo), (B) teflon i.v. cannula (Abbocath-T), and (C1) teflon i.v. cannula (Venflon); (C2) open collection system (acidwashed polyethylene tubes) + teflon i.v. cannula (Venflon). For each technique the first 5 ml of blood were discarded. No statistically significant differences were found between serum concentrations of nickel and chromium in specimens collected with the sampling techniques A, B, C1 and C2. This study has shown that identical results for concentrations of nickel and chromium in serum are obtained independent of whether a steel needle or a teflon i.v. cannula is used for blood sampling, provided the first 5 ml of blood are discarded. Likewise, identical results are obtained independent of whether specimens are collected in a closed or an open collection system, provided collection devices are acidwashed and sampling takes place under hospital conditions.