The transport systems for adenosine, guanosine, uridine, cytidine and thymidine were analyzed kinetically, physically and for a possible system of regulation in the fungus Achyla. Transport of nucleosides was inhibited by metabolic energy uncouplers, 2,4-dinitrophenol, carbonylcyanide-p-chlorophenylhydrazone, citrate (which chelate cell wall membrane Ca2+) and N6-substituted adenines (cytokinins) which displace 3 highly polyphosphorylated dinucleosides (HS3, HS2 and HS1) from a phosphorylated proteoglycan (PPG) attached to the cell membrane. Neither citrate nor the substituted adenines (except the nucleoside forms) entered the cell within the short period of transport measurements. Transport of nucleic-acid bases, adenine, uracil, cytosine and thymine was unaffected by these inhibitors of nucleoside transport. Nucleosides were probably transported without modification for they could be made to efflux unchanged after being concentrated inside the cell which was then poisoned with metabolic energy uncouplers. The optimum pH of transport for all nucleosides except guanosine was 6.5. Guanosine had 2 pH optima at 6.5 and 8.0. They (nucleosides) were transported optimally between 30.degree. and 40.degree. C, except thymidine which used a much higher optimum-temperature transport system. Osmotically shocked Achlya cells do not transport nucleosides but they do transport nucleic acid bases which are taken up by facilitated diffusion. Osmotic-shock treatment of cells released the membrane PPG with associated Ca2+ ions and HS compounds. When the PPG and HS compounds were relaid on the membrane, nucleoside transport was resumed by the cells. Possibly nucleoside transport and the PPG-Ca(II)-HS complex may be linked and concentrating the nucleosides in the cells may be an energy-linked activity.