Previous studies have indicated that examination of glycosaminoglycans (GAG) present in peri-implant sulcus fluid (PISF) may be a useful indicator of metabolic activity of the supporting bone. The GAG content in PISF from osseointegrated implants ad modum Brånemark in the maxilla was quantified and analysed. The study comprised 2 groups with 10 patients in each group. In one group the patients wore removable prostheses; in group 2 the patients wore fixed prostheses. The groups were matched for age, sex and function period of their prosthetic appliances. Clinical data were recorded, and the levels of the GAG hyaluronan (HA) and chondroitin-4-sulphate (C4S) were assessed using cellulose acetate electrophoresis and densitometric scanning of Alcian blue-stained strips against known GAG standards. PISF volumes and levels of C4S as potential bone marker showed no significant difference (both groups median 0.003 microgram). There was a somewhat higher median value for HA (0.015 microgram) in the group of patients with removable prostheses compared with the group with fixed prosthesis (HA = 0.008 micrograms) (NS). HA is known to be present in high amounts in gingival tissue. As both plaque index and gingival bleeding were more frequent in patients with removable prostheses, this may be the reason for the somewhat higher value for HA in this group of patients. The difference in biomechanical properties of fixed and removable prostheses on implants do not appear to be reflected in the bone responses as measured by GAG content in PISF.