The recent discovery that griseofulvin can be used orally as a fungistatic, effective against the dermatophytes, represents a major advance in therapy. In this country the majority of cases of ringworm are due to infection of the feet by organisms which can be controlled by topical fungicides, albeit with a high relapse rate. In recent years, however, there has been an increased incidence of infection by Trichophyton rubrum, a species which gives rise to resistant and intractable infections, especially when the nails are infected, and there would appear to be a small group of people in whom infection of multiple nails by this organism has hitherto been incurable. The preliminary papers of Williams, Marten, and Sarkany (1958) and Blank and Roth (1959) have shown that this organism, like the other dermatophytes, is inhibited in vivo by griseofulvin, and there would appear to be every likelihood that these infections may soon be controllable. Clinical experience of the drug is as yet too limited for a great deal to be known about the effective dosage, the duration of treatment required, the long-term results, and the possibility of toxic reactions. The following report records the experience of two independent groups of observers who have handled the drug during the last seven months. Of the 34 patients treated, 26 have had long-standing infection of multiple nails and skin by T. rubrum, previously resistant to numerous lines of treatment, including surgical avulsion of nails. In each case fungus has been demonstrated microscopically in the affected site and identified by culture prior to starting treatment. All patients have been examined and scrapings checked at regular intervals, and in 12 instances blood counts have been done daily for 14 days and thereafter at weekly intervals. In the following report an area is said to have cleared only when the clinical state has returned to normal and fungus can no longer be demonstrated microscopically or by culture ; in most instances photographs have been taken to compare changes in nail infection ; except in the group specified, no local treatment has been carried out.