The autoxidation reaction of diterpenic 4-axial-aldehyde torulosal (1b) has been studied. Naturally occurring 4-hydroxy-nor-diterpenes have been proved to be artefacts arising in the autoxidation of the corresponding 4-aldehyde. Hydroperoxides (1d) and (2d), the main autoxidation products of 1b, have also been postulated as intermediates in the formation of 4-hydroxy-nor-diterpenes (1a and 2a).