The hypothesis that contemporary metabolic pathways envolved from analogous chemical reaction sequences on the primitive Earth leads to a reexamination of models of prebiological phosphorylation. Present-day phosphate uptake by algae and bacteria seems to involve two transport systems: (a) A n active transport process occurring at low external phosphate concentrations (as in umpolluted natural waters), with a transport constant Ks of 10(-7) to 10(-6) M Pi. (b) Another (probably diffusive) process at higher phosphate concentrations (greater than 10-6 M)(as in the interstitial water of reducing sediments). Laboratory model experiments are described for the reation of reducing sugars with orthophosphate in the presence of cyanogen, producing glycosyl phosphates. These reactions proceed with appreciable yields only at high phosphate concentrations (greater than 10-3 M), and may thus possibly serve as simulations of prebiological phosphorylation with diffusive transport, as it may have occurred in the intestial water of reducing sediments.