The maximal response of a selection of ascorbic-acid-dependent parameters to a range of intakes of ascorbic acid has been shown to occur at virtually one level of intake in the present experiments. Further, this response occurred with intakes that produced only 1/2 saturation or less of tissues with ascorbic acid. Excessive intakes did not enhance effects, and, as in the case of serum copper levels, may have a detrimental effect. In view of the known factors that may influence requirements and the intralaboratory variability in experimental conditions, the more reasonable approach to the interpretation of dose response data is likely to relate the response to the accompanying degree of tissue saturation, rather than to an absolute level of ascorbic acid intake.