Serum transferrin and prealbumin levels were determined at intervals of 3 to 4 days in 16 patients requiring nutritional support. Caloric and nitrogen intake were measured and nitrogen balance calculated. There were 117 intervals available for analysis. A mean decrease in transferrin of 12.95 mg/dl was associated with a mean decrease in nitrogen balance of 0.92 g/day, whereas a mean increase in transferrin of 21.04 mg/dl was associated with a mean increase in nitrogen balance of 1.49 g/day; the correlation between changes in transferrin with changes in nitrogen balance was statistically significant (p = 0.02). Upward and downward changes in prealbumin were also associated with corresponding changes in nitrogen balance, but the changes were not statistically significant. Decreases in transferrin and prealbumin were also associated with a lower caloric intake. Operation caused a significant decrease in prealbumin (p = 0.003) and nitrogen balance (p = 0.05); a decrease in transferrin also occurred, but was not statistically significant. There was a highly significant correlation between serum transferrin and prealbumin (p = 0.001) and also between the interval changes in transferrin and prealbumin (p less than 0.001). In conclusion, transferrin was found to correlate closely with prealbumin. Changes in transferrin were more significantly related to changes in nitrogen balance, and from the results of this study, measurement of serum transferrin can be recommended as a useful parameter in following the nutritional status of patients receiving nutritional support.