Two different approaches for the numerical approximation of delay differential equations describing here the time evolution of biological systems are discussed. One of the numerical approaches is mainly designed to solve stiff problems and the other to solve non-stiff problems. Numerical codes are also referred to. One of the main goals of the authors is also to emphasize the main difficulties arising in the numerical integration of such delay differential equations compared to those based on ODEs. The method is applied to the Waltman model on antibody production based on equations with state-dependent-delays.
