Aging of the free-living nematode, Turbatrix aceti, has been accomplished by a procedure based upon screening of the cultures every 3--4 days to remove newborn organisms. In this system, the enzymes, isocitrate lyase, phosphoglycerate kinase and enolase all show reduced specific activities with age in crude homogenates. More critically, pure enolase shows a reduced specific activity when isolated from old compared with young organisms (958 units/mg vs. 1340 units/mg, respectively). Immunotitration experiments confirm these results. Enolase from old T. aceti requires more antiserum per unit of enzyme activity than does enolase from young organisms. This relationship holds true for both crude homogenates and pure enzyme. The above results closely parallel previous results obtained using fluorodeoxyuridine to prevent reproduction of T. aceti during aging of the organisms. Therefore, use of fluorodeoxyuridine in the aging of nematodes is perfectly safe, at least with respect to results obtained with altered enzymes.