Representative sections of the capsules that envelop surgically implanted silicone were analyzed for their collagen content. The specimens were biopsied (as incidental procedures) as the opportunities arose. All four classes of capsules as codified clinically and those surrounding tissue expanders are represented. The ages of the capsules ranged from 6 weeks to 13 years.Eighteen specimens were examined by slab gel electrophoresis. Type I collagen predominated in all of the electrophoretic patterns. Type III collagen was consistently present in lesser concentrations. Type V collagen was consistently present as a small fraction. There was no evident correlation between the concentrations of the component collagens and the clinically assessed class of the capsules or of those from around tissue expanders, but there was a correlation to the age of the capsules. The electrophoretic patterns of the collagens of this study are indistinguishable from the (previously reported) analyses of (cutaneous) scar.