Malignant pleural effusion (PE) is a frequent problem in lung cancer. In this study, we established a model of malignant PE of human adenocarcinoma cells, PC-14, in SCID mice. Intravenously injected PC-14 cells formed colonies in the lungs as early as week 4 after tumor inoculation, and produced bloody PE in all recipient SCID mice by week 8. Pretreatment of SCID mice with anti-mouse IL-2 receptor beta chain antibody (TM-beta 1) to deplete natural killer (NK) cells markedly promoted the production of bloody PE and metastases to multiple organs, such as the lungs, liver, kidneys, and lymph nodes 4 weeks after tumor inoculation. Histological studies indicated that PC-14 cells formed colonies in the lungs, and then invaded the pleura and spread to the pleural cavity. To establish cell lines with a high potential to produce PE, we harvested PE, expanded the tumor cells in vitro, and injected them into SCID mice again. By four in vivo selection cycles in this way we obtained PC-14-PM4 cells, which produce lung metastases and PE earlier than PC-14 cells. The survival of SCID mice inoculated with PC-14-PM4 cells was significantly shorter than that of mice inoculated with PC-14 cells. The expressions of adhesion molecules, such as CD44, CD49d, ICAM-1, and MHC class I, on PC-14-PM4 cells tended to increase compared with PC-14 cells. These changes of adhesion molecules seem to be one of possible mechanisms involved in higher metastatic potential of PC-14-PM4 cells. PE models with PC-14 and PC-14-PM4 cells should be useful for biological and preclinical studies on malignant PE produced by human lung cancer.