The isolated fat cell perifusion (P-IFC) system is used in conjunction with an automated analysis of glycerol (Technicon). The system is well suited to the study of "initiation" and "termination" of lipolysis. Glycerol release is initiated with epinephrine (EPI) and terminated passively by "buffer alone" or actively by insulin (INS) or proinsulin (PRO). Perifusion with "high" or "low" InS or PRO was performed, prior to, simultaneous with, or after infusion of EPI. Both hormone concentration and the sequence of administration greatly alter the responsiveness of adipose tissue to lipolytic and anti-lipolytic stimuli. Recently, we have demonstrated that non-hormonal agents, i.e., the nucleoside, adenosine, inhibits lipolysis and alters the responsiveness of the isolated fat to lipolytic stimuli. Identification of nucleoside was made by 1) high pressure liquid chromatography and 2) incubation with adenosine deaminase. Coupling of P-IFC to automated glycerol analysis greatly improves the reproducibility and sensitivity of the system, and increases the number of experiments that can be performed.