Orocaecal transit time was assessed in healthy cats and cats with hyperthyroidism by means of the breath hydrogen test using a standard liquid meal with lactulose. The median transit time in 10 healthy cats was 98 minutes (range 60 to 150 minutes) and 90 minutes (range 75 to 150 minutes) in a repeated assessment. The median transit time in 10 cats with hyperthyroidism was 53 minutes (range 45 to 150 minutes) which was significantly more rapid (P < 0.05) than in the healthy cats.