The interaction of four lectins from crops of the legume family with Saccharomyces cerevisiae alpha-mannan, and also with two glycoenzymes containing mainly alpha-mannan moieties, has been studied. The interaction was characterized by a quantitative precipitation assay. The results of precipitation differ with respect to both quality (the point of maximum precipitation) and of the quantity (the amount of aggregated lectin and saccharide). The lectin concanavalin A [Con A, from jack bean (Canavalia ensiformis)] was observed to form more extensive precipitates with Saccharomyces cerevisiae mannan and glycoenzymes than did lectins from Lens culinaris (lentil) and Pisum sativum (garden pea), while in the case of Vicia faba (broad or fava bean) no interaction was found with either the examined mannans or with glycosylated enzymes. The complete precipitation of invertase and glucoamylase with Con A (enzymes and also Con A; up to 100%) was achieved at a Con A glycoenzyme molar ratio of 20.2 and 2.3 respectively, whereby about 85% of precipitated and also of initial activities of glycoenzymes were determined in the aggregates. More valuable results were achieved by the technique of enzyme immobilization called 'multiple bioaffinity layering' which is based on the stepwise biospecific adsorption of the glycosylated enzymes and Con A on a matrix precoupled with Con A. A 3-fold repetition of the layering procedure afforded up to a 10-fold increase in catalytic activity of the immobilized invertase, in contrast with a 2.1-fold increase in catalytic activity of the immobilized glucoamylase.