Abstract Whole algal cell, phycobionts from Xanthoria parietina, Caloplaca citrina and Ramalina pollinaria, were immobilized onto the surface of wells of PVC microtiter plates. Two approaches were investigated: (a) immobilization via adsorption through ionic forces, viz., adsorption on polylysine-coated or cationized BSA-coated surfaces and (b) immobilization via covalent binding of cells onto chemically reactive surfaces obtained by coating the latter with BSA followed by activation with glutaraldehyde. To test the suitability of these systems for solid-phase binding assays, the immobilized cells were exposed to antisera against whole algal cells; bound antiserum was quantitated by the addition of 125I-PrA and counting. Non-specific binding of immunoglobulins to the modified PVC surfaces and the immobilized cells was efficiently blocked with normal goat serum. Of the systems studied, cells immobilized onto PVC microtiter wells, by either covalent binding or by electrostatic absorption to cationized BSA-coated surfaces, were found to be most suitable for solid-phase binding assays.