The content of tuliposides and tulipalins were determined in Tulipa species and cultivars by reversed-phase high-performance liquid chromatography (RP-HPLC), using a water:methanol gradient as mobile phase. The compounds were detected by a diode array detector employed at 208 nm. The investigation revealed, in addition to 1- and 6-tuliposide A, tuliposide D and the lactonized aglycones tulipalin A and (-)-tulipalin B, the new tuliposide F and 6-tuliposide B, the latter being a new acyl derivative of the known 1-tuliposide B. All compounds were isolated by preparative RP-HPLC and identified by NMR and mass spectroscopy. The predominant compounds were 6-tuliposide A and B present in amounts up to 1.5% and 1.3% of fresh weight, respectively. 6-Tuliposide A and tulipalin A seem to be the major allergens in tulips, although tuliposide D and F may also contribute to the allergenic properties. Tulipalin A and (-)-tulipalin B occur in intact tulips and are not only produced in response to fungal attack or after excision of the plants. A few species were found to have very low allergen content and a relatively high level of tuliposide B, indicating it should be possible to breed non-allergenic and disease-resistant tulips.