The various isozymes of human alcohol dehydrogenase have been examined by Blue Sepharose column chromatography. 2. The products (alpha, beta1 and gamma1) of the common alleles at the three ADH loci (ADH1 ADH2 and ADH3 respectively) were found to show slight, but significant differences in their affinities for Blue Sepharose. The order of affinity of the homodimeric isozymes was: alphaalpha less than gamma1gamma1 less than beta1beta1. The heterodimeric isozymes showed intermediate affinities. 3. The products (gamma1 and gamma2) of the common alleles (ADH31 and ADH32 respectively) at the ADH3 locus showed a pronounced difference in their affinities: the gamma1gamma1 isozyme was firmly adsorbed by Blue Sepharose, whereas the gamma2gamma2 isozyme was not adsorbed. The heterodimeric gamma1gamma2 isozyme was intermediate in its behaviour. 4. The 'usual' and 'atypical' forms of ADH were indistinguishable by Blue Sepharose column chromatography. 6. The 'anodal' form of ADH showed no affinity for Blue Sepharose.