1. Crude synaptosomal fractions obtained from four areas of rat brain were studied; cerebral cortex, hippocampus, midbrain, thalamus with hypothalamus, using the Cotman & Matthews method (1971) Biochim, biophys. Acta 249, 350-394. 2. The purity of synaptosomal fractions was controlled by electron microscopy, and by determination of some marker enzymes such as: LDH, MAO, AChE and cytochrome-c oxidase. 3. Synaptosomes were disrupted by hypoosmotical shock. 4. Crude synaptosomal membrane preparations indicated on increased Ca2+ Mg2+ -ATPase activity in comparison to the activity of this enzyme in synaptosomal fractions. 5. The incubation of crude synaptosomal membranes with cAMP and theophylline caused the subsequent increase of Ca2+ Mg2+ -ATPase activity, but mainly, in hippocampal region.