Transducer-protector device for biomedical haemodialysis lines comprising a first and a second element each of which is formed in a single piece of moulded plastic material with a tubular fitting and an annular radial flange. The first element is formed with a semi-crystalline polymer and the related annular radial flange has greatly thinner portions able to allow the see-through viewing of the filtering membrane secured between the flanges of the first and of the second element.