We have been attempting to localize and characterize adenylate cyclase and cyclic nucleotide phosphodiesterase in Euglena. Adenylate cyclase activity appears to be present in fractions containing microsomes, flagella, and propolastids. With the exception of the flagella fraction, the fractions were not very pure. Cyclic nucleotide phosphodiesterase seems to be located within the pellicle and is more specific for cyclic GMP than cyclic AMP. The pH optimum of the Euglena phosphodiesterase is similar to that found in mammalian phosphodiesterases. We plan to further characterize the pellicle phosphodiesterase and flagella adenylate cyclase. Also we intend to study the effect of varying growth conditions, e.g., light, different fixed carbon sources, on the activities of these enzymes.