The development of the first standardized "scratch 'n sniff" olfactory test is described. Over 1600 subjects participated in five experiments. In Experiment 1, 50 microencapsulated odorants were rated as to their intensity, pleasantness, irritation, coolness, and familiarity, and two procedures for releasing them were compared. In Experiment 2, the results of the first experiment and other data were used in the development of the test, which was administered to a large number of subjects. Using multiple regression analysis, scores on this test were shown to be significantly related to the subjects' gender, ethnic background, and smoking behavior. Average test scores decreased as a function of age, with the greatest decline occurring between the sixth and tenth decades of life. These age-related changes were not correlated with scores on the Wechsler Memory Scale. Women performed better than men within all age categories. In Experiment 3, the test was shown to differentiate between subjects with known olfactory disorders (e.g., Kallmann's syndrome; Korsakoff's syndrome) and normal controls, and to reliably detect persons instructed to feign total anosmia. In Experiment 4, the test-retest reliability was established (6-month interval; r = 0.918, p less than 0.001), and in Experiment 5 the test was shown to correlate thresholds with odor detection (r = -0.794, p less than 0.001). This self-administratered test now makes it possible to rapidly and accurately assess general olfactory function in the laboratory, clinic, or through the mail without complex equipment or space-consuming stores of chemicals.