Complex animal model system. I. Liver metastasis (I.a) / colonisation (I.b) model. Human xenograft colon cancer cell suspensions (HT29, HCT116 and HT25) were intracolonic and intrasplenic injected to scid mice; C26 mouse isograft colon cancer cell suspension was injected into Balb/C mice. In proper „metastasis” system the whole metastatic sequence is represented, while „colonisation” model represents just the later part of metastatic cascade. II. Spontaneous lung metastatsis model of subcutaneous (heterotopic) tumour injection: single cell suspension of human xenograft colon cancer was injected into adult and newborn scid mice. Primary tumours were grown in both cases, while pulmonary metastases were produced only in the newborn.