SummaryThirty patients suffering from all types of seizure, were treated with this drug.1) Mysoline was exceedingly effective in controlling grand mal epilepsy, but it was especially ineffectual against petit mal. In treatment of psychomotor and focal epilepsy, none was completely controlled, but some of these showed marked reduction in seizures.2) A remarkable effect of mysoline was observed in some patients who had shown a very poor response to any other kinds of anticonvulsants.3) Favourable results were obtained by the use of mysoline alone or in combination with other anticonvulsants, and eight cases of them showed better result when mysoline was reinforced with phenylmalonylurea or 3, 5, 5‐trimethyloxazolidine‐2, 4‐dione, as well as by reduced dosage of the drug.4) Some of its side effects were found in a good many patients, but mostly mild and temporary, except some acute toxic influences. No dangerous toxic effects have so far been encountered in our investigation. These acute toxic effects were most probably caused by constitutional hypersensitiveness against this