Collagen composition in tissue capsules around implants has been reported to differ histologically from collagen in subcutaneous connective tissue. In the present study, an immune histochemical analysis of collagen types I and III was undertaken in tissue capsules of various implant materials. The materials included polyvinyl chloride/polyacrylonitrile copolymer, poly(ethylene terephthalate), polysiloxane, titanium, and hydroxyapatite, which had been implanted into the dorsal subcutaneous space of rabbits for various time periods from 28 and to 90 days. The results indicate that collagen type III stained in all capsules independent of the evaluated materials, implantation periods, and material surface roughness. Collagen type I stained only in titanium implant capsules and dominated there over collagen type III. The staining sensitivity was highly specific and reproducible. The presence of collagen type III can be expected because it is the collagen of connective tissue healing. Collagen type I appears to be a response to chemical or electrochemical titanium surface properties but not to surface roughness. The quantitative relationship between the two collagen types may indicate capsule tissue stability and therefore serve as another biocompatibility measure.