It is often of importance in a psychiatric department to ascertain whether a patient has consumed the Largactil prescribed, e.g. on occasions when a patient appears only to be slightly affected by Largactil. Dubost and Pascal demonstrated that a Largactil solution mixed with equal quantities of concentrated sulphuric acid gives a marked carmine red colour which is so stable that the intensity of the colour may be measured in a spectrophotometer. In biological fluids, Largactil must first be extracted with ether and then transferred to the aqueous phase before the determination can be undertaken. By experiments on rabbits and dogs, these authors found that up to 5 per cent. of the Largactil administered is excreted in the urine in the course of 24 hours and a total of up to 8 per cent. is excreted in the course of the first few days.