Life spans, growth rate, glucose utilisation, response to hydrocortisone, and intracellular activity of lysosomal N-acetyl-beta-glucosaminidase of rheumatoid synovial cells in culture were compared with these properties in nonrheumatoid synovial cells. Except for a small group of RA cells derived from tissue explants, the cells were all isolated by trypsinisation of synovial tissue, either within intact joints or after synovectomy. Cell lines were established by passaging with trypsin. In a study of 56 nonrheumatoid and 24 rheumatoid synovial lines isolated during a 7-year period the latter were found to have a shortened mean life expectancy in culture, though there was wide variation between individual lines. This is in agreement with reported findings from untrypsinised explant-derived synovial lines. However, in the present study mean multiplication rates were identical for nonrheumatoid and rheumatoid synovial cells, and on clear differences could be demonstrated for the other properties studied. No correlation could be found between the life spans of synovial cell lines and the age of the cell donors, whether from rheumatoid or nonrheumatoid sources. Rheumatoid synovial cells isolated from intact joints were notable for especially high proportions of macrophage-like cells and suppression of fibroblasts. In most cases cell lines could not be established from these rheumatoid primary cultures, and in others the lines were short-lived. Early association with relatively high proportions of macrophage-like cells in rheumatoid cultures might thus be important in influencing the establishment and behaviour of synovial cell lines.