In a pilot study (I) the efficacy of a new combination therapy for hair loss of the diffuse type was tested in 36 patients, followed by a double blind study with 47 patients. The daily dosage was 18,000 IE retinol, 70 mg L-cystine and 7000 mg gelatin. The clinical efficacy was evaluated by standard methods, such as the preparation of trichograms and measurement of the hair density before and after treatment. The pilot study demonstrated a significant improvement, with reduction of the telogen rate by 8.3%, an increase of the anagen rate by 11%, and an increase of the hair density by 6.9%. In the double blind study (II) the trichogram showed a significant decrease of the telogen rate by 13.5% compared with pathological baseline values. There was no change in the placebo group. The lowered anagen rate of 47.2% was improved by 8%, whereas the mean value in the placebo group decreased from 47.7% to 39.9%. In addition, the percentage of dysplastic anagen hairs improved by 7.4%, as against further impairment with an increase of 26% in the placebo group. During oral therapy no systemic side-effects were detected. We conclude that long-term oral therapy with high doses of L-cystine and gelatin in combination with vitamin A may have beneficial effects on diffuse hair loss.