The purification of a phosphate-binding protein (PiBP2) by immunoadsorption is described. The entire anti phosphate-binding protein 2 antibodies as well as the Fab fragments obtained from these antibodies inhibit Pi uptake by whole cells. The inhibition is a mixed type of inhibition (Vm and Km are affected). These results should be regarded as a possible involvement of phosphate-binding protein 2 in Pi uptake. The binding of 125I-labelled fragments prepared from anti phosphate-binding protein 2 antibodies to whole cells, to shocked cells and to protoplasts has been investigated. The results confirm the release of phosphate-binding protein by osmotic shock and during protoplast formation. From these findings, a cell-wall localisation, near the cell surface of the phosphate-binding protein should be proposed.