Genomic RNA was transcribed in vitro from the non-infectious Sindbis (SIN) virus expression vector (pTRCAT) and introduced into C6/36 (Aedes albopictus) cells by liposome-mediated transfections. The chloramphenicol acetyltransferase (CAT) polypeptide expressed within cells was detected by an indirect immunofluorescent assay directly into 24-well polystyrene tissue culture plates. Approximately 1 in 1000 C6/36 cells showed fluorescence when the transfection was optimized. CAT enzyme activity was also assayed; in C6/36 cells CAT expression was detected as early as 8 h after transfection, peaked at 24 h, and could still be detected at 7 days. At 24 h posttransfection each transfected C6/36 cell was calculated to express 1.3 x 10(7) CAT polypeptides.