The generation times and synthesis of glycosaminoglycans (GAGs) of three normal and five rheumatoid synovial fibroblast strains were studied. Wide variations were observed between strains in their growth and synthesis rates. In general, the normal strains grew more rapidly than the rheumatoid ones and their GAG synthesis, studied by a 3H-glucosamine labelling technique, was also more active. The distribution of newly synthesized hyaluronic acid and sulphated GAGs was studied in incubation media, pericellular matrix and the cells. The rheumatoid cells seemed to retain less newly synthesized GAGs in their pericellular matrix than did the normal cells. The effects of cortisol on GAG synthesis were studied in these strains at cortisol concentrations ranging from 1 × 10−8 M to 1 × 10−5 M. Attention was also paid to the distribution of newly synthesized GAGs among the three fractions mentioned above. Cortisol inhibited the synthesis of GAGs by both normal and rheumatoid cells even at 1 × 10−7 M, normal cells being the more sensitive. The inhibiting activity of the steroid on GAG synthesis was not linear. A cortisol concentration of 1 × 10−6 M was just as inhibitory as 1 × 10−5 M. However, even though overall hyaluronic acid synthesis was reduced at 1 × 10−6 M cortisol the relative amount of newly synthesized hyaluronic acid in the pericellular matrix of rheumatoid cells increased.