Abstract: A method for reducing the pressure in and then collecting medium samples in containers such as test tubes sealed by a resilient stopper at substantially atmospheric pressure, comprising piercing the stopper at or shortly before the time of collection of a medium sample by a first cannula, connected at one end to a pressure-reducing device, thereby connecting the interior of the container with the pressure-reducing device via the first cannula; evacuating the container to a desired subatmospheric pressure; withdrawing the first cannula; penetrating the stopper by a second cannula connected at one end to a medium source to be sampled, thereby connecting the source with the interior of the container via the second cannula; and then sucking a sample of medium into the container under the influence of the subatmospheric pressure effected in the interior of the container by the pressure reduction.