The formation of aniline from sodium salt of 6-hydroxy-5-(phenylazo)-2-naphthalenesulphonic acid (SS-AN, C.I. 15970, Orange RN), a subsidiary colour in the Japanese colour additive Food Yellow No.5 (Y-5, C.I. 15985, Sunset Yellow FCF), was investigated in the artificial gastric fluid (AGF) and in the artificial intestinal fluid (AIF) as prescribed in the degradation test in the Japanese Pharmacopoeia (1996). Aniline concentrations of 0.3–6.8 μg/ml were found in 0.1% SS-AN solutions with 0.1–5.0% ascorbic acid or erythorbic acid after 24h at 37°C. This simulates a mixture of dye and ascorbic acid that might be ingested. The amount of aniline generated depended upon the temperature in these systems. In systems to which sucrose had been added, an increase in the amount of aniline generated was observed. However, no aniline generation was observed in the 0.1% SS-AN solutions in the AGF or AIF at 37°C for 24 h. Furthermore, the generation of aniline was not seen in AGF and AIF at higher temperatures in the range of 37–80°C. It was not generated by the degradation of SS-AN in the presence of digestive enzymes.