This study investigated the effect of glutaraldehyde on the synovial tissue of rabbits. Four different concentrations of glutaraldehyde solution were injected into one knee and the contralateral glenohumeral joint of rabbits in group A to group D. The concentration levels used in group A and group B were 1000 ppm and 100 ppm, respectively. For group C and group D, samples of rinsing solutions obtained by rinsing arthroscopic equipment with 1 1 or 2 1 of isotonic saline, respectively, after immersion in 2% glutaraldehyde were used. The contralateral knee and ipsilateral glenohumeral joint of the same rabbits were injected with saline and used as control sites. Rabbits were sacrificed after 1 day, 7 days or 15 days and the histopathological changes in the synovial tissues were compared. The most dramatic inflammatory changes were observed in group A and group B. The histopathological changes were-greater after 7 days than after 1 day or 15 days. Group C and group D showed no significant differences when compared with normal synovium. A correlation between the concentration of the glutaraldehyde solution and the number of inflamed joints was observed. Very few or no inflamed joints were seen when samples from rinsing solutions of 11 or 2 1 of saline, respectively, were used.