A method is presented for measuring growth of bacteria under high hydrostatic pressure in subsamples taken without pressure change in the incubation vessel. Subsamples may be withdrawn rapidly (5 s) and are not subjected to shear forces. Vice versa, nutrient media, labeled substrates, etc., may be introduced into the culture while under pressure. Chemical fixation of subsamples for electron microscopy or adenosine 5'-triphosphate determinations under pressure is also possible without affecting the growing culture. Data are given of growth experiments demonstrating the feasibility of the method. Problems of oxygen depletion are discussed.