Brouwer et al1 have developed country-specific crop-exposure matrices (CEMs) for the French Agriculture and Cancer Study (AGRICAN) and the Cancer in the Norwegian Agricultural Population (CNAP) Study to enable data pooling with another study included in the AGRICOH consortium,2 the US Agricultural Health Study (AHS), for which self-reported pesticide use information is available. External data were not available to validate the exposure assessment methods, but self-reported use in the AHS was compared with exposure estimated using CEM approaches resembling those developed for AGRICAN and CNAP. Poor agreement with self-reported use in the AHS was shown for 11 pesticide active ingredients, and the CEM approaches had very low specificity (not reported, but calculated to range between 25% and 42%). More importantly, the CEM approaches also appear to greatly overestimate exposure when applied in their own cohorts. Nevertheless, the investigators state that these exposure assessment methods will be applied in other AGRICOH pooling projects including an investigation of lymph-haematological cancer and pesticide exposure. They acknowledge …