Treatment of buffalo calves (Bubalus bubalis) at different times after birth demonstrated that transmission ofToxocara vitulorumfrom the cow to the calf via milk occurs in all calves during the first 2 days after birth, decreases to 53% by 6 days, 10% by 8–9 days and 2% from Day 10 onwards. This may be because the larvae are no longer in the milk or because the calf has become resistant to the establishment of a new infection. The result also emphasizes the importance of mammary transmission of the parasite. Against immature parasites the efficacy of pyrantel and levamisole was 97%; febantel was 100% on one farm, only 35% on another; piperazine 42% and thiabendazole 35%. Santonin was ineffective in four calves. Against mature parasites the efficacy of pyrantel was 100%; febantel was 100% on one farm, only 35% on another; oral levamisole 83%; cutaneous levamisole 73%; oxfendazole 89%; and piperazine 57%. Nevertheless, piperazine reduced the infection to levels which were probably not pathogenic. In general, the efficacy against mature parasites was similar to that against immature parasites. Treatment of 10–16‐day‐old calves with an anthelmintic, which is effective against immature parasites, is recommended. This procedure greatly reduces contamination of the environment and also precludes the pathogenic effect of a large number of immature or mature pa