The article presents the methodology of non-destructive tests of adhesively bonded metal sheets using active thermography, illustrated with an example of selected imperfections related to the application of adhesive. The experimentation involved the design and the making of specimens reflecting actual car body joints with simulated imperfections such as the complete lack of or the insufficient amount of adhesive between two sheets. The research also involved the selection of a measurement technique, the development of a testing procedure and the manner of interpreting thermographic test results in the form of recorded sequences of images. The thermographic tests were performed in a two-sided arrangement, where a specimen was situated between a heat source and a thermographic camera. Such an arrangement enabled the uniform heating of the specimen surface and, as a result, the obtainment of legible images used for determining the maximum temperature contrast. The test results made it possible to assess the size and approximate shape of the layer of adhesive between two sheets of analysed lap joints. This article constitutes the continuation of previously initiated works dedicated to the development of active thermography related to non-destructive tests of permanent joints.