The invention relates to a method for non-destructive error diagnosis of composite components provided with metallic or ceramic foam core making it possible to detect errors inside the core with a high certainty although said foam core exhibits heterogeneous properties. For this purpose, according to said invention, the composite element provided with the metallic or ceramic foam core is connected to elements by material fit on at least two opposite sides and the elements are made of a homogenous material at a constant sound speed. At least one actuator which makes it possible to inject ultrasound waves having predetermined frequency into the composite element is mounted on the external surface thereof. A sound detector is mounted at a predetermined distance from the actuator on the surface of the opposite element and makes it possible to determine, in each case, the time required in order to a predetermined threshold value of the detected measuring signals of the ultrasound waves is exceeded. In addition or alone, the maximum value of the absolute value of the detected measuring signals of the ultrasound waves can be determined during a time interval between the beginning of the injection of the ultrasound waves and a prederminable moment.