RESUMEN
The controlled release of drugs is an appealing area of research as it provides numerous benefits in veterinary and human medicine. In this paper we attempt to analyze certain aspects related to topical drug delivery systems, their successes and failures, and their place in veterinary medicine. Some emphasis is given to the pharmaceutical aspects of the delivery systems, where the material available made it possible. Purely topical devices, such as cattle ear tags and various collars, as well as some topically administered bioavailable delivery systems are discussed. Special attention is given to hitherto under-evaluated delivery systems, such as topical varnishes. A carefully selected bibliography aims to lead the reader easily to the facts, without providing overwhelming data of varying quality. We believe that the paper may be of interest to practicing veterinarians as well as to pharmaceutical scientists working or considering practice in the area.