(1) An account is given of a serious infestation in sheep and lambs by Ixodes ricinus in the uplands of Denbighshire, North Wales.

(2) This infestation was accompanied by serious disturbance of health resulting in the general deterioration of the flock and the death of lambs.

(3) Experimental dippings were commenced in 1924, using a special “short-interval” arsenical dip supplied by the Cooper Technical Bureau, London. Serial dippings were made each spring at five-day intervals. When possible an early autumn series was conducted.

(4) The objects were (a) to control the infestation, (b) to control the diseased condition, and (c) to attempt to eradicate ticks from the land.

(5) The control of both the ticks and the disease were easily effected. A few sporadic cases of disease did occur during the course of the experiment.

(6) Eradication has not yet been accomplished, but the average number of ticks was reduced from 121 per animal in May 1924 to 0-96 per animal in July 1926.

(7) It is therefore suggested that short-interval dipping for serious tick infestation in sheep is practicable on British hill farms, and that resultant mortality from disease can thereby be reduced.