Abstract: Apparatus is disclosed for withdrawing and collecting samples from a pressure vessel without disturbing either the reaction pressure contained within the vessel or the physical conditions of the sample which is extracted. A tubular probe having a perforated end is contained in a sealable second tube capable of attachment to an operating reaction pressure vessel. The probe is capable of sliding into the pressure vessel and withdrawing a sample of material from the pressure vessel without disturbing the reaction contained therein. The probe is capable of withdrawing the sample material and collecting it in the sealable second tube, which can be removed and carried away to analyze the samples.