In a previous study, the authors identified that lectin purified from Helianthus tuberosus belongs to a group of lectins referred to as mannose/glucose-binding lectins and that this lectin has a high affinity for α-linked manno-oligosaccharides. This study further reveals that HTA exhibits an even higher affinity for mannan from S. cerevisiae than a-linked manno-oligosaccharides. It was also demonstrated that HTA agglutinates yeast cells possessing　mannan on their surface. The optimum concentration of　HTA for agglutinating S. cerevisiae was shown to be about 1.0 mg/ml. Twenty-two strains of yeast were agglutinated at various levels of HTA. The agglutinating activity induced by HTA remained nearly constant in a pH range of 6.0 to 8.5, but decreased drastically as pH was reduced from 6.0 to 5.0.