The in vitro invasiveness of LA1, LAD, LA5 variants of mouse lung adenocarcinoma (LA795) with different metastatic potentials were examined. Precultured heart fragment (PHF) was used as the target organ, and spheroid aggregates of LA1, LAD, LA5 cells were prepared by cultivation of cell suspension on a gyratory shaker. The invasion-complex was formed by confronting of the PHF and cell aggregate. The invasion-complex was then examined at different time intervals histologically and morphometrically. The micro-computer-aided image analysis system was employed to measure the total area (TA) of the invasion complex and the tumor tissue area (subarea, SA). The ratio of SA/TA was used in estimating the invasion ability. It was shown that the invasion of LA1, LAD and LA5 was progressive in nature and the invasive capability of these three variants were correlative with their metastatic potentials.