RP is an exaggerated vasospastic response to cold or emotion. Randomized, double-blind, placebo-controlled trials with either parallel group or cross-over trials should be mainly considered. Cross-over design, which is good for early phase trials of immediate or very short-term outcomes, is important in a condition as heterogeneous as RP: a wash-out period between treatment arms should always be included to minimize the possibility of a period (carry-over) effect. Duration of RP trials is usually constrained by the need to complete these over a single season, usually winter when the weather is colder. For cross-over trials, each treatment arm tends to be 4 weeks or less. Frequency and duration of attacks, and the Raynaud's Condition Score are widely used outcome measures. There is increasing interest in physiological laboratory endpoints, for example laser Doppler imaging at least for early phase trials.