The relation of serum albumin concentration to age was assessed in a series of hospitalized medical patients. Those with disease states (e.g., dysproteinemia, renal insufficiency, hepatic dysfunction, malnutrition) potentially associated with abnormal serum albumin levels were excluded, leaving a study population of 11,090 patients. The mean serum albumin concentration fell progressively with each decade of age, from 3.97 gm/100 ml in subjects aged less than 40, to 3.58 gm/100 ml in those aged 80 or older (F greater than 50.0, P less than .001). The percentage of patients with a normal serum albumin level (4.0 gm/100 ml or higher) also decreased progressively with age, whereas the frequency of a low serum albumin level increased with age. Sex, primary diagnosis, blood urea nitrogen concentration, duration of hospitalization, and geographic location of the hospital did not influence the findings. The reduced serum albumin concentration in the elderly could contribute to age-dependent changes in the clinical effects of certain albumin-bound drugs, since pharmacologic activity can be influenced by the extent of albumin binding, in turn related to albumin concentration.