The most effective biocide used historically in antifouling paints is tributyltin (TBT). However, due to its extreme toxicity to non-target organisms and its persistence in the environment, the use of TBT and other organotin compounds (OTCs) was restricted in EU on leisure boats and ships in 1989 and 2003, respectively. Nevertheless, studies worldwide still report TBT to be released from both ships and leisure boats. Here, we present a new application for a field portable X-ray fluorescence spectrometer (XRF) used for screening for organotin paint through measurements of tin (Sn) on leisure boats and ships. Measurements on ships built after the restrictions showed concentrations of up to 68 mu g Sn/cm(2), likely due to impurities of inorganic Sn, as shown through chemical analysis of 21 organotin-free paints. A threshold value of 100 mu g Sn/cm(2) is suggested, where exceedance indicates presence of OTCs. Screening with the XRF method showed 10% of the commercial vessels (n = 30) and 23-29% of leisure boats (n = 693, investigated in this and in a previous study) to hold concentrations exceeding 100 mu g Sn/cm(2). The XRF technique presented here provides a useful tool for quick screening and identification of vessels holding banned organotin paint.