Spheroids are three-dimensional cell aggregates expressing histotypic organisation in vitro comparable to tissue continuity in vivo. They can be prepared from normal tissue and from tumour fragments. In the experiments presented here, dermal human spheroids and brain tumour spheroids are prepared from the same patient. The dermal tissue originates from the border of the incision wound made to effect a stereotactic brain tumour biopsy. The tumour originates from a fragment of the collected stereotactic biopsy. The dermal fragment and the brain biopsy are explanted in vitro to form confluent monolayers. At confluency, the dermal cells are transferred into small Erlenmeyer flasks and rotated at 37 degrees C for 1-2 days and rotation mediated spheroids are formed. Small flaps of the tumour monolayer are placed on a semisolid non-adhesive substrate, reorganise and form agar overlay spheroids. After spheroid formation, a dermal spheroid is confronted with a brain tumour derived spheroid. The confronting pair, after adhering to each other, present an invasion model in vitro. The dermal spheroid functions as the autologous host for the brain tumour spheroid. Putative invasive cells present in the reaggregated brain spheroid will invade the dermal spheroid and destroy it. If no invasive cells are present in the tumour derived spheroid no morphologic changes will be seen in the dermal spheroid; 24 tested brain biopsy spheroids demonstrated a clear correlation between malignancy in situ and invasiveness in vitro. So it can be concluded that the autologous confrontation of brain tumour derived spheroids with dermal spheroids derived from the patient has a predictive value concerning malignant evolution and mimics the situation of the tumour in situ.