Photodegradation kinetics of four nitro musks (musk xylene, musk tibetene, musk ketone and musk moskene) in solid-phase microextraction (SPME) fibres ("photo-SPME") and in an aqueous system were studied by means of gas chromatography-mass spectrometry (MS) detection. Musks fragrances were extracted from aqueous solutions using SPME fibres that subsequently were exposed to different UV irradiation times, generating photoproducts easily characterized by their mass spectra. Aqueous photodegradation studies followed by SPME were also performed and compared to photo-SPME. The same fourteen photoproducts have been detected in both media. The potential of this approach to readily calculate apparent rate constants (from 10(-4) to 10(-3) s(-1)), half-life times (from 3 to 32 min) and reaction orders (n = 1) in both media is stated. The main photoreaction determined was photocyclization, but products of photoreduction and photorearrangement have also been detected. Tentative photodegradation pathways for musk moskene and musk tibetene are proposed for the first time.