Mitospores or cysts of Allomyces macrogynus do not take up the glucose analogue 2-deoxyglucose. Uptake of 2-deoxyglucose by germlings begins at 25 min into germination, the start of the rhizoid stage, and increases in rate by approximately 50-fold until 100 min into germination. The rate remains constant from 100 to 200 min, at which time germination is completed and hyphal formation begins. The presence of glucose in the germination medium blocks the uptake of 2-deoxyglucose. Of the other sugars tested, only galactose had any effect on 2-deoxyglucose uptake. Actinomycin D treatment during germination in a glucose-containing medium prevented the appearance of the uptake system, but actinomycin D was not effective after the transfer to a glucose-free medium. Cycloheximide treatment prevented the appearance of the uptake system if it was added at the time of the transfer to the glucose-free medium; it inhibited uptake only partially if the germlings were starved of glucose before its addition. It appears, therefore, that both ribonucleic acid synthesis during germination and protein synthesis after the removal of glucose are required for the uptake of 2-deoxyglucose.