Deltamethrin (IR, 3R)-3(2,2-dibromovinyl)-2, 2-dimethylcyclopropane carboxylate of (S)-alpha-cyano-3-phenoxy-benzyl, was observed in the field in Zambia to offer a better residual effect against adult Rhipicephalus appendiculatus of up to 7 days post-treatment during a high infestation pressure period than on organophosphorus (OP) acaricide. A group of 20 cattle sprayed with deltamethrin wash of approximately 0.005 w/v at 14 days intervals carried an average of less than 12 ticks per head by the 7th day post-treatment, whereas two groups of 20 cattle each, dipped weekly in an OP at 0.05% w/v had an average of over 60 ticks per head. In a theileriosis infected area 14 days' treatment with deltamethrin would probably be unsuitable for disease control during high infestation period, but 7–10 days would probably yield better results than those likely to be obtained with OPs.