In a first study we confirm the general evidence concerning the influence of implicit knowledge structures on sentence and text comprehension. In addition the results suggest a differentiation in the availability of prior knowledge. The level of activation is dependent on the type of semantic relations between prior knowledge and the explicit sentence information. This result can be explained by a theoretical framework in which different levels of cognitive effort can be related to activation or production of such relations. The main point of our second experiment is to prove the influence of aging on the process of knowledge integration mentioned above. We compared the results of a subject group of young (25 years) with old adults (75 years) in a recognition task. The experimental data support a slowdown for primarily sensorical and motorical and nonlexical components for the higher age group but they do not confirm a deficit in the critical process of knowledge integration. Finally we discuss a differentiation of such integration procedures dependent on demand of memory capacities (activation vs. operations) and the advantage of such a classification on identification of specific cognitive deficits.