A new standardized precision needle which virtually removes operator variation from skin prick testing with allergens is described. The instrument is simple and robust, and the results of its use are demonstrated. The most important finding was that the use of strong pollen extracts produced very inconsistent and irregular weals, but when suitably diluted, or used on mildly sensitive skins, reproducibility of the response was excellent and it is therefore ideal for titration of skin sensitivity and biological assessment of the potency of allergens. The standard needle was also compared with two other methods of skin prick testing. Results were similar but the standard needle showed the least variation.