Nine clinically healthy men, 41–47 yr of age, served as subjects in a 24-hr study conducted at the Edward Hines Jr Veterans Administration Hospital in the Chicago area in May 1988. Physiologic measurements, and blood and urine samples were collected at 3-hr intervals over a single 24-hr period beginning at 1900. The number of variables measured or calculated (total = 98) included: 6 vital signs (oral temperature, pulse, blood- and intraocular pressures); 16 in whole blood (counts and differentials); 50 in serum (SMAC-24, lipids, hormones, electrophoresis of LDH and proteins); and 26 in urine (solids, proteins, creatinine, catecholamines, melatonin, Cortisol, electrolytes and metals). Data were analyzed for time effect by analysis of variance (ANO VA) and for circadian rhythm by single cosinor. Individual rhythm characteristics for each variable were summarized for the group by population mean cosinor. The vast majority of variables revealed statistically significant within-day changes in values as validated by one-way ANOVA. All vital signs (except for intraocular pressures) and all serum hormones displayed a prominent circadian rhythm for the group, as did most variables in whole blood, while only about half of the variables in urine demonstrated a significant group rhythm. The results obtained are meant to: (a) document the circadian time structure; and (b) serve as reference values for circadian rhythm characteristics (range of change, mesor, amplitude and acrophase) for a defined group of individuals: clinically-healthy adult men in the prime of life.