The light induced degradation of nitromethane, nitroethane, 1-nitropropane and 2-nitropropane in the gas phase (Fujiki-Test) and adsorbed on silica gel (GSF-Test) was studied. It was found that light induced degradation in the gas phase is significantly faster. 14C-labelled compounds were used in the case of reaction on silica gel. A new method for microsynthesis of the nitroalkanes is described.