Four isolectins were isolated from bulbs of Croccus sativum (saffron), using affinity chromatography on mannan-Sepharose 4B, gel filtration and ion-exchange column chromatography in the presence of 8 M urea. The relative molecular masses of these lectins were determined by gel filtration to be approximately 48 kDa. On polyacrylamide gel electrophoresis, relative molecular masses of 8 kDa were obtained, suggesting that the lectins are hexamers. No carbohydrates were detected in the lectins. The lectins agglutinated the yeasts of Saccharomyces cerevisiae at a minimum concentration of 30 micrograms/ml, however, they did not agglutinate animal erythrocytes (human, sheep, rabbit and mouse) even at a concentration of 1000 micrograms/ml. In inhibitory experiments, mannan from Saccharomyces cerevisiae was the most potent inhibitor of C. sativum lectins. While D-mannose showed no inhibition, manno-oligosaccharides with either (alpha 1-2, 1-3) or (alpha 1-6) linkages were potent inhibitors, suggesting that C. sativum lectins recognized manno-oligosaccharide units larger than mannobiose. Ovomucoid also exhibited potent inhibition, however, the other carbohydrates examined did not.