Complement proteins naturally occurring in mammalian sera mediate cytolytic events, contract smooth muscles, and activate lymphocytic and myeloid cells.  Heat-inactivation destroys the activity of complement in serum.  This method is therefore recommended for immunological applications and for the culture of embryonic stem cells (ESCs), insect cells and smooth muscle cells.
The heat inactivation process must be carefully controlled to prevent denaturation of desirable serum proteins that are key constituents of sera necessary for cell and tissue propagation.
Heat inactivation occurs when serum is heated to 56 °C for a period of 30 minutes.