Method for fluid rotation with three-dimensional hydrodynamic focusing in a two-layer chip system, in which channel segments are introduced alternately into the upper and the lower substrate in such a way that, after the two chip layers have been connected, the previously open channels are closed to form microchannels by the surface of the respective other chip layer and a connection to the next channel segment exists only at the ends of the microchannels, at fluid transport velocities with Reynolds numbers Re < 10, in which the medium to be rotated passes through microchannels which are arranged one behind the other and are connected to one another and are arranged at an angle to one another, as a result of which the medium flowing through in each case undergoes changes in direction which, overall, cause the medium to rotate about the axis in the direction of flow, the fluid flow being rotated about the flow axis by an angle α in each case as it flows through the channel transitions between the microchannels, which angle α depends on the channel geometry and on the angle β between the channel segments, characterized in that • the microchannels are designed with a semicircular channel cross-section, • the fluid passes through six channel transitions bent at an angle β of 32 degrees to one another, the angle of rotation α of the fluid lamella in the individual transitions not being uniform but rather dependent on the bending angle β and the respective orientation of the incoming lamella, so that a total of six rotations of the fluids take place and the total angle of the fluid rotations in the sum of the partial angles results in 90 degrees • and that before the fluid rotation a hydrodynamic focusing is carried out, in which the supply of auxiliary fluids is carried out with such a pressure that a fluid lamella oriented perpendicular to the chip plane is produced, which is rotated about the flow axis by the fluid rotation, and after this fluid rotation, which is set to 90 degrees, a second hydrodynamic focusing is carried out, whereby the homogeneous fluid lamella aligned parallel to the chip plane is reshaped, in which in the second hydrodynamic focusing unit the supply of the auxiliary fluids is carried out with such a pressure that the fluid lamella aligned parallel to the chip plane is slightly compressed in order to obtain a homogeneous fluid lamella which is not influenced by the channel walls, so that it is in particular kept free from the channel walls. • the microchannels are designed with a semicircular channel cross-section, • the fluid passes through six channel transitions bent at an angle β of 32 degrees to one another, the angle of rotation α of the fluid lamella in the individual transitions not being uniform but rather dependent on the bending angle β and the respective orientation of the incoming lamella, so that a total of six rotations of the fluids take place and the total angle of the fluid rotations in the sum of the partial angles results in 90 degrees • and that before the fluid rotation a hydrodynamic focusing is carried out, in which the supply of auxiliary fluids is carried out with such a pressure that a fluid lamella oriented perpendicular to the chip plane is produced, which is rotated about the flow axis by the fluid rotation, and after this fluid rotation, which is set to 90 degrees, a second hydrodynamic focusing is carried out, whereby the homogeneous fluid lamella aligned parallel to the chip plane is reshaped, in which in the second hydrodynamic focusing unit the supply of the auxiliary fluids is carried out with such a pressure that the fluid lamella aligned parallel to the chip plane is slightly compressed in order to obtain a homogeneous fluid lamella which is not influenced by the channel walls, so that it is in particular kept free from the channel walls. <EOS>