The invention concerns reagent delivery system for an apparatus for processing of biological samples arranged on microscope slides, comprising a reagent section having one or more reagent containers; a slide section in which at least one microscope slide is arranged; a probe for dispensing a portion of reagent onto a predetermined microscope slide, and means for handling the probe. The probe comprises a continuous prove tubing element extending through a rigid probe member and connecting the probe tip to a pneumatic pressure regulation device. The reagent containers are adapted for cooperation with the probe tip. In this manner a high though-put and a very low carry over of fluid residues is achieved since there is no assembled parts making up the inside volume of the probe in which the fluid may be retained.