A double-blind placebo-controlled study of the effect of inositol nicotinate (Hexopal) in the treatment of Raynaud's phenomenon is described. Sixty-five patients, 20 males 45 females, aged 18-75 years, weighing 40-100 kg were enrolled by 45 General Practitioners in East Anglia, Scotland and North Midlands. They were given either Hexopal or placebo 4 × 500 mg tablets twice daily for three months. The two groups were well matched for pre-treatment characteristics and well balanced for environmental temperature during the trial. After six weeks' treatment 14 out of 29 patients in each group had improved but at the end of the study 21 in the Hexopal group (78% of those remaining) had improved whilst the number in the placebo group remained at 14 (56% of those remaining). A statistically significant improvement in symptoms and reduction in frequency of Raynaud's attack was seen only in the Hexopal group. Compared with placebo, symptoms were significantly better with Hexopal after three months of treatment. This study, conducted as far as possible under natural conditions in the cold season, produced further confirmation that Hexopal not only reduced the severity of Raynaud's symptoms but also the frequency of Raynaud's attacks.