An automatic sampler of fine needle aspiration biopsy for cytology (FNAC) is presented in order to study the technical performance of FNAC in vitro. The effects of the following sampling technique variables on specimen size and quality can be independently and quantitatively studied: suction force, duration and rate of increase of suction; count, frequency, amplitude and angle between the needle strokes; length, diameter, content and tip configuration of the needle; and target tissue. The efficacy of the sampler was compared with a manual method. It was demonstrated that the poor reproducibility of manual FNAC, combined with inaccuracy in following instructions regarding changes in sampling technique, render the manual system unsuitable for quantitative studies. The clumsiness of the manual system may be responsible for contradictory recommendations on how FNAC should be carried out. With the new in vitro sampler FNAC sampling can be studied under fully controlled conditions.