Dermatitis in 8 female nursery workers handling Alstroemeria ligtu cultivars has been proven/proved in 6 cases to be of allergic origin. Epicutaneous tests with cut flower extracts as well as with the isolated and purified sensitizer were positive. Successful animal experiments corroborated the sensitising capacity of Alstroemeria cultivars. The responsible but unstable contact allergen, alpha-methylene-gamma-butyrolactone (tulipalin A), was found in short ether extracts of flower petals in concentrations up to 18%. Due to its instability, subsequent extractions were performed with methanol, yielding the sensitising constituent after purification in the glucosidic form (tuliposide A). This could be stored at room temperature for longer periods without loss of activity. Tuliposide A was determined in specimens of Alstroemeria ligtu cultivars of 14 different origins of various colours; its content varied between 1 and 2%. Direct testing of the plant material in human patients carries the risk of false positive reactions and active sensitisation, as the threshold for both forms of the allergen is very high. Only a concentration of 0.01% can be considered safe.