  We study the pattern dynamics in a reaction diffusion model of the
activator--inhibitor type in the oscillatory regime. We consider finite systems
with partially absorptive boundary conditions analizing examples in different
geometries in one and two dimensions. We observe that the boundary conditions
have important effects in the pattern forming properties of the systems. In all
the studied cases, the arising complex behaviour is found te be dependent on
the absorption parameter. By changing this parameter we can control the
asymptotic behaviour to be stationary, periodic, quasiperiodic or chaotic.
