It has long been customary to use a single large dose in the treatment of worms in animals, but in man there has been a tendency to use a course of doses, especially in the treatment of threadworm. In the case of phenothiazine when used against threadworm the division of the dose has probably been undertaken in order to avoid toxicity. There is, however, no definite evidence that the toxic hazard is reduced in this manner, in fact, it may well be increased as with poorly absorbed substances greater absorption is obtained with the presentation of the treatment over a longer period. This can be clearly demonstrated in laboratory tests.