The adhesiveness of Balb/c 3T3 cells partially synchronized either by drug treatment or by the mitotic cell shake‐off procedure was assessed by following the aggregation kinetics of aliquots of the cells suspended under defined conditions within the confines of a cone and plate viscometer. M phase cells synchronized by either method were significantly more adherent than appropriate control cells. Cells arrested in S phase following drug treatment were found to be poorly adhesive whereas G1 phase cells prepared by allowing drug treated M phase cells to proceed through mitosis or by treating them with L‐histidinol did not differ in their adhesiveness from appropriate control cells. The adhesiveness of control cell populations was found to vary with the extent of re‐feeding indicating a possible metabolic dependency of cell adhesion. It is suggested that although M phase cells are poorly adherent to the substrate they are nevertheless considerably adherent in an aggregation system. There was no apparent correlation of the observed increase in intercellular adhesion with any particular stage of M phase (prophase, metaphase, anaphase, telophase). We propose that Balb/c 3T3 cells show an increase in cell‐cell adhesiveness as they proceed into M phase and that this is maintained until after division is complete. Our suggestion that certain cell types may interact differently with each other and with the substrate in different stages of the cell cycle could have in vivo relevance in those processes such as tumour spread where considerable cell division is involved.