A description is given of a bioreactor (1), in particular for NMR spectroscopy, comprising a container (7) capable of containing a cell culture, a first inlet line (6) for the inward flow of a culture medium to the inside of the container and a second outlet line (9, 10) for the outward flow of the culture medium from the container (7). The first line (6), an inlet line, is connected to a spiral-shaped device (12) which has a form such that when the medium is made to flow inside the first line (6) and made to flow out of the second line (9; 10), hydrostatic thrust and hydrodynamic forces produce with respect to the cells a condition of simulated reduced gravity inside the container (7).