Experimental investigations have been carried out in 32 children on the therapeutic effect of griseofulvin in favus caused by Trichophyton schoenleinii and to determine the optimal treatment schedule.It was found that, while daily doses of 3.12 mg, 6.25 mg or 12.50 mg griseofulvin per kg of body-weight did bring about a measurable degree of inhibition of the fungal hyphae in infected hairs, a dose of 25 mg/kg daily for some 28 days was required to effect complete cure. The advantages of greater daily doses (50 mg/kg) were not sufficiently pronounced to justify the extra cost involved. Administration of doses under 50 mg/kg on alternate days is unsatisfactory, as it allows for the re-establishment of the hyphae in newly formed keratin.Another favourable schedule is the administration of 50 mg/kg daily for five days, thus setting up a stable and impenetrable griseofulvin barrier, followed for about 28 days by daily doses of 6.25 mg/kg that would otherwise be subtherapeutic but in this case prevent the reintroduction of infection from extrapilar fungi.