The spectrum of OsO4 has been measured in the vapour and in solution. Detailed structure reported in the main absorption bands by Langseth and Qviller was not reproduced. The irregularity of the main intervals between peaks, and their sensitivity to temperature, bespeak a perturbed spectrum which is too diffuse to analyse convincingly. Three fragmentary systems of quite different appearance were observed in all samples and could well be weak forbidden transitions. The spectrum of RuO, vapour is no better resolved. Reproducible features of both spectra are tabulated.