A catheter for insertion into the human body and which includes one or more optionally scanning ultrasonic transducers (7) and a needle guide, which can be operated from the outside and used for collecting tissue samples from the human body. The catheter includes two substantially semicircular parts (2, 3), where a rod (4) is inserted between said parts and at the end is provided with an ultrasonic transducer (7), said two semicircular parts (2, 3) being kept together by means of an outer tube (5) passed over the two semicircular parts (2, 3), and where the surface of one semicircular part (2) is provided with a longitudinal groove (6) for the insertion of a flexible needle (12) for the extraction of tissue samples. The resulting catheter is very user-friendly and easy to disassemble for disinfecting and sterilizing purposes.