Critical anthelmintic tests and controlled trials were used to assess the efficiency of laevo‐tetramisole hydrochloride against nematode infections in sheep and cattle. In sheep, oral dose rates of 5 mg/kg and above were 94 to 100% effective against adult Haemonchus contortus, intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbianum, O. venulosum and Chabertia ovina. A dose rate of 7.5 mg/kg was required for consistently high activity against Ostertagia spp, but activity against Trichostrongylus axei remained variable at this dose level. Efficiency against Trichuris ovis ranged from 76 to 100% at a dose rate of 10 mg/kg. The drug was 94 to 100% effective against 7‐day old and 14‐day old H. contortus, intestinal Trichostrongylus spp and O. colun bianum infections, and 83 to 89% effective against 14‐day old Ostertagia spp and T. axei, at a dose rate of 5 mg/kg. Seven‐day old Ostertagia spp larvae were highly resistant at a dose rate of 10 mg/kg, while activity against T. axei infections of the same age appeared variable at 5 and 10 mg/kg. In cattle, subcutaneous treatment at dose rates of 1.5 mg/kg and above, and oral treatment at 7.5 mg/kg, were 93 to 100% effective against adult Haemonchus placei, intestinal Trichostrongylus spp, Nematodirus helvetianus, Cooperia spp and Oesophagostomum radiatum, and 84 to 98% effective against Ostertagia ostertagi. Against Trichostrongylus axei, a rate of 5 mg/kg subcutaneously was 83% effective, and a rate of 7.5 mg/kg orally 97% effective, while these dose rates gave 88 to 100% clearance of adult Dictyocaulus viviparous. Copyright © 1969, Wiley Blackwell. All rights reserved
