The stability of pilocarpine hydrochloride in ophthalmic solutions after heating and storage, and the influence of light and of two types of containers on stability, have been investigated. Pilocarpine was assayed by a modification of a published method. In ophthalmic solutions sterilised by heating to 100° for 30 min. it is stable for at least one year at 15–25° in the dark in bottles of good quality glass covered with a nylon cap. The stability of ophthalmic solutions containing pilocarpine and eserine during storage and after different methods of sterilisation was also investigated. This solution can be heated at 100° for 15 min. and, stored in suitable bottles, it is stable for at least 18 months.