  In this article we have successfully obtained an exact solution of a
particular case of SIR and SIS epidemic models given by Kermack and Mckendrick
[1] for constant population, which are described by coupled nonlinear
differential equations. Our result has no limiting conditions for any parameter
involved in the given models. In epidemiology many researchers believe that it
is very hard to get an exact solution for such models. We hope this solution
will be an opening window and good addition in the area of epidemiology.
