To gain an insight into the tissue reactions leading to noninfectious loosening, 25 autopsy specimens of acetabula with well-fixed cemented sockets were analyzed histomorphologically and morphometrically. The mean duration of the implant was 7 (0.2-16) years. With the exception of some focal direct bone-cement contacts, bone and cement were separated by a soft tissue membrane which increased in thickness with increasing duration of the implant. Necroses in the membrane were also commoner with advancing implant time. The soft tissue membranes developed increasingly dense infiltrates of histiocytes, mainly containing wear particles of the bone cement and--though less abundant--polyethylene. The cancellous bone adjacent to the soft tissue membrane showed an increasing histiocytic infiltration with an increasing duration of the implant. The trabecular bone showed remodeling with formation of a neocortical layer parallel to the border of the cement mantle.