Abstract: A process and apparatus for the withdrawal of samples from a reaction vessel under pressure containing a solid-liquid dispersion, emulsion, or suspension sensitive to mechanical stress, wherein a portion of the liquid consists of a liquefied gas present in the emulsion, dispersion, or suspension in a dissolved or emulsified form, as for example, the withdrawal of samples during the manufacture of polyvinyl chloride in accordance with the suspension or emulsion method. A syringe and cannula combination are filled with an inert protective fluid with the cannula being passed through a valve arrangement in the reaction vessel to eject the protective fluid thereinto and to replace the ejected fluid with a sample from the reaction vessel. The sample-containing syringe is sealed before withdrawal of the cannula of the combination from the reaction vessel, which is again sealed by the valve arrangement.