Satisfactory performance in interlaboratory proficiency tests for the determination of metals in sediments does not necessarily demonstrate that laboratories' data are of adequate comparability. This paper reports a study of the comparability of sample preparation techniques (i.e. drying grinding, sieving etc., prior to sample digestion) for the determination of metals in marine sediments. The results indicate that that the particular requirements of the task in hand may need to be emphasised, if adequate comparability is to be achieved. Recommendations for quality control in sample preparation are made.