Histologic assessment as well as information about the disaccharidase activity of the small intestinal mucosa can be useful in the management of patients with small intestinal mucosal damage. In an effort to determine whether the degree of small intestinal mucosal damage would be reflected in a corresponding reduction in disaccharidase activity, we compared small intestinal mucosal histology with the results of disaccharidase activity measured in per oral suction small intestinal biopsies obtained from 21 infants with protracted diarrhea. The degree of small intestinal mucosal damage was graded using a subjective score (i.e., 0 to 4+ damage) by a pathologist (P) and by a computer-assisted digitizing system (to assess villus surface area, VSA, and villus/crypt ratio, V/C) in a blinded fashion. The mean (+/- SD) age of the infants was 2.5 +/- 1.5 months, and the duration of diarrhea was 25.2 +/- 11.5 days. There was good correlation between the results obtained from the digitizing system and from the pathologist: VSA versus P, r = 0.695; V/C versus P, r = 0.791; p = 0.0004. All infants demonstrated some degree of small intestinal mucosal damage. The mean (+/- SD) values for P, VSA, and V/C were 2.2 +/- 1.3, 2.9 +/- 0.9, and 0.9 +/- 0.5, respectively. The mean values for lactase, sucrase, and maltase were 17.1 +/- 17.0, 71.1 +/- 54.0, and 224.3 +/- 233 mumol/min/g protein, respectively. No correlation was observed between the histologic scoring results and lactase, sucrase, or maltase measurements. Expressing the disaccharidase activities per unit wet weight of tissue did not improve the correlations. Log transformation of the data also failed to improve the correlations.(ABSTRACT TRUNCATED AT 250 WORDS)