The left gastric artery was cannulated in 17 cats, and a single dose of microspheres was injected into the artery, after which it was ligated. Microspheres with diameters of 8-10 micrometer induced gastric mucosal erosions that healed within 1-2 weeks. Microscopic examination revealed that there were few microspheres in the submucosa, more in the muscularis and large numbers in the glandular layer. The muscularis mucosae was intact. After injection of 50 +/- 5 micrometer spheres a large gastric ulcer developed. The ulcers healed after 4 weeks. Microscopically, the ulcer penetrated through the muscularis mucosae, and many microspheres were seen in the submucosa and serosa beneath the ulcer.