  The 3D Ising-like system in the external field is described using the
non-perturbative collective variables method. The universal as well as
nonuniversal system characteristics are obtained within the framework of this
approach. The calculations are carried out on the microscopic level starting
from the Hamiltonian. They are valid in the whole $h-T$ plane of the critical
region. It is established, that the contributions related with wave vector
values $\vk\to0$ exhibit the properties of the total system near the critical
point. The behaviour of the susceptibility as function of the temperature in
the presence of the field is investigated. The locations of the maximums
susceptibility on the temperature scale for different values of the field are
established.
