Wound contraction is a clinically important biological process because it frequently results in contractures, strictures, and stenosis. If Collagen synthesis could be altered to minimize the contracture, then the outcome could be improved. Lathyrism produces poorly cross-linked Collagen in healing anastomosis, keeping a larger portion of the synthesized Collagen soluble. Ultimately, the amount of contracting Collagen is reduced, lowering the bulk and lessening the contracture. The aim of this study was to observe the effects of a lathyrogen, beta-aminoproplonitrile (BAPN), on the healing of colonic anastomosis. Thirty rats were divided into three groups. Colostomy and anastomosis were performed on all rats. Intraperitoneal saline solution (control) and either intraperitoneal (ip) or oral (po) BAPN were administered. The rats were killed I week later. Anastomotic healing was assessed by bursting pressure and the hydroxyproline content of the anastomotic tissues. Granulation tissue thickness number of fibroblasts inflammatory cells, and growing capillaries in granulation tissue per unit area were determined. Collagen fibril diameters were estimated, and spatial arrangements of fibrils were examined by an electron microscope. All results were evaluated by Mann-Whitney U-test. The analyses of anastomotic tissues from BAPN-treated rats showed a significantly reduced mean bursting pressure (158.9 +/- 12.3, 171.3 +/- 13.9, ip and po, respectively), hydroxyproline content (8.9 +/- 2.6, 10.1 +/- 2.7), granulation tissue thickness (24.3 +/- 2.6, 16.1 +/- 5.2), number of inflammatory cells (37.8 +/- 4.3, 25 +/- 4.3), fibroblasts (3.2 +/- 1.1, 2.8 +/- 0.7), and a significantly reduced Collagen fiber diameter (15 2, 20 3) compared with those of control group (236.9 +/- 9, 14 +/- 4.4, 26.8 +/- 4.8, 39 +/- 2.6, 6.9 +/- 1.1, and 35 +/- 5, respectively). As a result, Collagen fibers were flimsy, and lost their regular parallel alignment in the BAPN groups. On the other hand, a number of growing capillaries were found to be significantly increased in these groups (16.5 +/- 1.1, 18.2 +/- 0.7) compared to the control (6.7 +/- 1.3). Thus, it is suggested that BAPN may be useful in the prevention of gastrointestinal stricture formation.