ABSTRACT Time-lapse microphotography was used to film the locomotory behaviour of cockroach haemocytes in vitro, and the cell tracks were analysed for speed and persistence; the percentage mobilization and the diffusion rate of the population were calculated. Haemocytes are either fast locomotor or spread moving cells, or non-motile spread or rounded cells; the first three types are plasmatocytes and their behaviour is interchangeable. Approximately 20% of the cells are motile under control conditions and there is no correlation between orthokinesis and klinokinesis. If activated haemocyte lysate supernatant (HLS), a source of components of the prophenoloxidase enzyme sequence, is added to the cell monolayer, up to 80 % of the cells switch to fast locomotor behaviour, rounding up and moving faster and for longer in straight lines. Neither heat-inactivated HLS nor zymosan supernatant, used to activate HLS, had any effect. If the chemokinins present in activated HLS are also released in vivo on haemocyte activation or during cuticular wounding, then they and the induced changes in haemocyte adhesion could contribute to haemocyte recruitment to sites of infection.