Samples from 67 manufactured lots of FD&C Yellow No. 6 (Sunset Yellow FCF; Colour Index No. 15985) were analysed for combined benzidine. These samples were selected from those submitted to the US Food and Drug Administration for certification between October 1991 and December 1992 by 13 dye distributors. Dithionite was used to reduce any combined benzidine present in the form of azo or disazo dyes to free benzidine. This reduction was followed by extraction, diazotization and coupling with 2-naphthol-3,6-disulfonic acid disodium salt (R salt). The total benzidine was quantified as benzidine-R salt disazo dye by HPLC with detection at 540 nm and a quantification limit of 10 ng benzidine/g FD&C Yellow No. 6. Of the 67 samples analysed, 34 were found to contain more than 10 ng combined benzidine/g. Of these, 30 samples were from one manufacturing company, including three of its subsidaries. The level of combined benzidine found ranged from 11 to 104 ng/g, except for one sample containing 941 ng/g.