The efficacy of 3 kinds of alphamethrin-impregnated ear tags was tested against natural Amblyomma hebraeum, Boophilus decoloratus, Rhipicephalus appendiculatus, and Rhipicephalus evertsi evertsi infestations of cattle. One type of ear tag was also tested in combination with a tail band of similar material. Ticks were counted macroscopically on their predilection sites. Counts of B. decoloratus, R. appendiculatus, and R. e. evertsi on all trial animals diminished steadily during the first 7d after application of the devices. Counts on untreated control cattle had returned to their pre-treatment levels by Day 14 in the case of B. decoloratus, and by Day 21 for R. appendiculatus. R. e. evertsi did not regain their pre-treatment numbers during the trial period on the controls, but did so on one of the treated groups. This temporary drop could be interpreted as being the result of pyrethroid contamination from the hands of the investigators at the time of applying the ear tags, but did not interfere with the assessment of the effect of the tags. None of the forms of treatment showed acceptable efficacy against B. decoloratus. Ear tags alone were not very effective against R. e. evertsi, but the numbers of these ticks on the perineum were diminished by the use of tail bands. Two kinds of ear tags showed superior efficacy against R. appendiculatus, and in the case of these, one ear tag appeared to be as effective as two. The effect against A. hebraeum was evidently influenced by the distribution of the impregnated devices. Two types of ear tags were used alone and had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)