Three distinct glycosyltransferases have been isolated and partially purified from anthers of Tulipa cv. Apeldoorn. The following designations are proposed; UDP-glucose: flavonol 3-O-glucosyltransferase (GT-I), UDP-rhamnose: flavonol 3-O-glucoside rhamnosyltransferase (GT-II) and UDP-xylose: flavonol 3-glycoside xylosyltransferase (GT-III). The three enzymes exhibited an identical pH optimum within the range of 8.5 -9.0. The estimated molecular weight of GT-I and GT-II was about 40 000, GT-III showed a molecular weight of 30 000. GT-III required ions like NH 4 + or Ca 2+ whereas these ions have almost no influence on GT-I and GT-II activity. The enzymes have a slight requirement for SH-reagents, particularly DTE. As opposed to GT-II activity of GT-I and GT-III is significantly influenced by SH reagents and PCMB. Sucrose enhanced GT-III activity but only slightly GT-I activity, GT-II activity is not influenced. Flavonol aglycones can function as glycosyl acceptor for the GT-I, whereas flavonol 3-O-glycosides, luteolin, dihydroquercetin, naringenin, cyanidin, p-coumaric acid and some other phenols were inactive as acceptor. The best acceptors were isorhamnetin and quercetin (Km: 0.9 × 10 -6 ᴍ). GT-II did not accept aglycones as substrates. For this enzyme flavonol 3-O-glucosides were the most attractive substrates. GT-III did not have any affinity towards aglycones, too. This enzyme exhibited a high specificity for flavonol 3-O-glucosides as well as flavonol 3-O-galactosides. Both enzymes, the GT-II and GT-III, were able to glycosylate flavonol 3-O-diglycosides forming triglycosides. UDP-glucose (K m = 1.0 × 10 -4 ᴍ), UDP-rhamnose and UDP-xylose where shown to be the best glycosyl donors for GT-I, GT-II or GT-III respectively. The glycosyl transfer catalysed by the GT-I was shown to be a freely reversible reaction. In the whole anthers, highest specific activities of GT-I and GT-II were found during late stages of anther development. Similar results were obtained using the contents of anthers or the tapetum fraction. In contrary, high GT-III activity can be detected already in young stages of anther development. The highest activities of the three glycosyltransferases were found in the tapetum fraction, whereas the pollen fraction exhibited only poor activities.