The phosphate (P-i)-binding protein PstS is a member of a family of periplasmic proteins that act as high-affinity receptors for active transport systems in bacteria. PstS protein purified from Pseudomonas aeruginosa was immobilized to N-hydroxysuccinimide-activated Sepharose, packed into a plastic column (5 x 70 mm), and examined for its potential ability to remove P-i from water. The PstS-Sepharose column completely removed P-i from P-32-labeled pond water containing about 0.5 muM P-i (0.015 mg P per liter). More than 90% of P-32-P-i that was retained in the column could be eluted by washing with low-pH water.