The effect of dusting with a commercial sulphite-based anti-melanosis formulation on several chemical quality indexes of Norwegian lobsters (Nephrops norvegicus) was evaluated and compared with a control batch during chilled storage. Dusting with 6% of the commercial product did not exceed the SO2 residual levels permitted by the EU Directive and by the Food and Drug Administration. The additive retarded successfully the occurrence of black spots on the crustacean surface for at least 7 days and also bleached the samples. The prior addition of the sulphite-based compound did not affect either muscle pH or total volatile basic nitrogen content during storage, although it did produce increased lipid oxidation. The protease activity decreased, and differences in the pool composition of proteases were observed, so serine and cysteine protease activities showing an increase. Finally, the sulphite-based compound delayed agmatine production and exerted an antimicrobial effect on H2S producers and Enterobacteriaceae.