A new strategy for characterisation of airborne uranium contamination based on elemental/isotopic analysis of tree bark is described. Bark samples collected at Tokai-mura (Japan) were subjected to high sensitivity ICP mass spectrometric analysis; for control purposes, samples from the remote Yakushima island (Southern Japan) and central Tokyo were also analysed. The uranium contents of tree bark for Tokyo and Yakushima were of similar magnitude to that at Tokai-mura (U, 0.01-1.0 μg/g - all samples), however, there were marked differences in isotope ratio values between the sites. Whereas natural uranium isotope ratio values (235U/238U, 0.0072) were observed for Yakushima and Tokyo, non-natural and natural signatures (235U/238U, 0.00697-0.01448) were realised at Tokai-mura. These findings are consistent with the release of enriched uranium at Tokai-mura.