In the course of experiments on the transmission of horse-sickness and blue-tongue of sheep [ cf. preceding paper], it was found necessary to evolve methods for rearing mosquitos, feeding them on experimental animals and keeping them alive in South Africa, where adverse climatic conditions, particularly the low humidity, proved to be the most important obstacle. As previous experience on this subject was of little real value, the methods had to be worked out from the beginning, and a somewhat detailed account of observations and results is given as a guide for future workers. The paper is divided into four sections, the first of which deals with the catching of adult and larval mosquitos. The second gives the methods used for keeping mosquitos alive in the laboratory and includes a description of a rack holding two tiers of cages in which a high humidity was maintained by running water on to the metal top of the rack, allowing it to soak the hessian with which the rack was covered and. draining the excess away by means of gutters round the base. Methods of feeding mosquitos on horses are described in the third section, which also shows the arrangements for attaching cages to the horses by means of elastic bands attached to a girth or by inserting them in holes in a specially constructed metal, saddle. Details are given of a special insect-proof stable in which the horse is prevented from lying down and a high humidity is maintained by means of walls of hessian kept wet in a manner similar to that used for the cages. When feeding mosquitos on sheep, the subject of the last section, the cages were held in position by tapes tied to locks of wool [ cf. R.A.E. B 22 171], and sufficient moisture was supplied by covering the tops of the cages with damp cotton-wool held in position by the same tapes.