SINCE the introduction of tetraethyl pyrophosphate as a miotic substance for treatment of primary glaucoma by topical administration,1 this drug has been employed in the treatment of several times as many patients as those described in the first report, and enough additional information has been obtained to warrant a follow-up note. Accordingly, a summary of experiences with a representative group of 60 cases is presented. The drug was administered, as described in the original paper,2 only to patients whose intraocular pressure was unsatisfactorily controlled by pilocarpine or physostigmine in the customary doses. If, after an adequate trial, tetraethyl pyrophosphate proved ineffective, administration of this drug was discontinued. However, if tetraethyl pyrophosphate was effective, its administration was continued but was interrupted from time to time for comparative trials of other miotics. This was done with the thought that a new drug, such as tetraethyl pyrophosphate, should achieve a place