Silver chloride containing fibers, spheres and particles of irregular form is used as a model material to study plasticity in metal matrix composites. Matrix dislocations generated upon cooling by the mismatch of coefficient of thermal expansion between the matrix and the reinforcement are observed by transmission optical microscopy after decoration at room temperature by photodissociation of the matrix. The plastic zone around the fibers, spheres and particles takes two forms: (a) trains of coaxial prismatic dislocation loops punched into the matrix and (b) a plastic zone of irregular form containing partially resolved tangled dislocations. A relationship between the inclusion volume and the volume of the plastic zone around a spherical or cylindrical inclusion in a strain-hardening matrix is presented and compared with experimental data. This relationship is extended to particles of irregular form.