Ultrasound scattering on biological, arbitrary-form structures is considered. Methods of integral equations by volume and surface integration are used in the task. The methods allow one to explore scattering from the surface and volume of arbitrary pathological insertions. A method of small perturbations is used. In the first approximation the weak-reflecting pathology is accepted. It is noted that pathology form and value appreciably affect echosignal and spectrum structure. In particular, echosignal spectrums for less dense and denser pathologies vitally are notable. The proposed method allows one to classify the pathologies of bio-organs. Sufficient agreement with theoretical models if shown experimentally on the weak-reflecting object (rubber).