The efficacy of milbemycin oxime against fourth-stage (L4) larvae and adults of Ancylostoma tubaeforme was investigated in a trial involving 24 young domestic shorthair cats. The animals were inoculated with approximately 300 infective stage three (L3) larvae and divided into three groups. After 12 days, eight cats (group 1) were treated with medicated tablets containing 4 mg milbemycin and 10 mg praziquantel to test the efficacy against L4 larvae; eight cats in group 2 were treated with the same tablets after 33 days to test the efficacy against adult worms; and eight cats in group 3 were treated with a placebo tablet. Faecal egg counts were determined periodically in each cat and after 40 or 41 days the number of worms in each animal was determined postmortem. The egg count reduction was determined by comparing the geometric mean numbers of eggs per gram of faeces in the placebo and medicated groups, and the worm reduction by comparing the geometric mean numbers of worms. The egg count reduction was more than 99 per cent in both treated groups, while the number of worms in groups 1 and 2 were reduced by 94.7 per cent and 99.2 per cent, respedively.