The reproductive performance of 25 male Irish wolfhounds was examined in a two-year follow-up study. Results of a previous study showed that 37 Irish wolfhounds had lower libidos, smaller testicles and poorer semen quality than 67 control dogs examined. This study was undertaken to determine whether fertility parameters had changed after a further two years. Forty-four dogs of 21 breeds were used as controls. No change in libido was observed in either group after two years; the Irish wolfhounds still exhibited lower libidos than the control dogs. In both studies, the Irish wolfhounds showed a softening of testicular tissue with a significantly higher incidence than control dogs. This difference became more marked after two years. Semen quality had declined in Irish wolfhounds and the differences between the two groups became more accentuated. Inbreeding coefficients for the Irish wolfhounds were low, suggesting that this was a factor contributing to the poor reproductive function. However, several Irish wolfhounds had been ill during the follow-up period which, together with the decline in reproductive efficiency, may reflect a change due to ageing.