Tributyltin and its metabolites were determined in environmental samples by gas chromatography using a flame photometric detection method. The analytical method involved the propylation of the organotins and the use of a recovery standard to correct for inefficient recovery. A detection limit of 5 ng Sn l(-1) for seawater, and 5 ng Sn g(-1) for sediments, was obtained when the detector was equipped with an optical filter; however, this concentration limit, which is higher than the environmental quality standard for TBT, could be improved by a factor of 100 on removing the filter. The limitations imposed by the choice of recovery and internal standards were discussed and it was shown that the possible presence of Sn(II) had no effect on the total extractable inorganic tin, as determined by the analytical protocol. The identification of unexpected mixed methylbutyltins in TBT-contaminated sediments was described, and the implications of the existence of such compounds were discussed.