The concentration of taurine in the aqueous humour and serum of 21 rabbits with hereditary buphthalmia (Bu rabbits-genotype bu/bu) was compared with the aqueous and serum taurine levels of eight strain-related normal rabbits (JAX) and nine non-strain-related normal rabbits (MCV). There was a significant difference in the mean aqueous taurine concentration in each of the three groups. The Bu rabbits had only 29% of the MCV rabbits' level while the JAX rabbits were intermediate with 56% of the MCV level. It is suggested that some of the JAX rabbits may be heterozygous and the Bu rabbits homozygous for a semi-dominant allele of a gene that is less efficient in taurine transport in the ciliary epithelium than the normal allele represented by the MCV animals.