Efficient increase of apoptosis incidence in rheumatoid arthritis (RA) synoviocytes by administration of recombinant FasL adenovirus (Ad-FasL). The percentage of apoptotic cells in grafted RA synovium in severe combined immunodeficiency (SCID) mice is compared to that in the RA synovium three days after treatments with Ad-FasL, LacZ adenovirus (Ad-LacZ) and PBS. Total synoviocytes and apoptotic cells were counted in 10 high power fluorescent microscopic fields randomly selected from each section, and three sections at multiple layers for each sample were examined. The percentage of apoptotic cells was recorded and is represented as the mean and standard deviation for each group. Open bars represent the percentage of apoptotic cells in RA synovium two weeks after engraftment without treatment; striped bars represent the percentage of apoptotic cells in RA synovium three days after Ad-FasL, Ad-LacZ and PBS injections.