In this book we consider a Cauchy problem for a system of ordinary differential equations with a small parameter. The book is divided into th ree parts according to three ways of involving the small parameter in the system. In Part 1 we study the quasiregular Cauchy problem. Th at is, a problem with the singularity included in a bounded function j, which depends on time and a small parameter. This problem is a generalization of the regu larly perturbed Cauchy problem studied by Poincare 35]. Some differential equations which are solved by the averaging method can be reduced to a quasiregular...