Abstract: The invention relates to apparatus for spiral plating of microorganisms on a growth medium for making a viable cell count. The apparatus comprises means (2) for rotating a plate (3) containing growth medium, an inoculator (7) adapted to expel inoculum onto the growth medium, means (8) for moving the inoculator along a radius of the plate as the plate rotates so as to deposit inoculum along a spiral path on the growth medium, means for exerting a force on the inoculator such that the inoculator can continuously keep contact with and follow contours on the growth medium, and means (4) for controllably varying the rate of expulsion of inoculum along the spiral path. The invention also relates to an improved inoculator assembly, apparatus for controllably varying the rate of depression of a syringe plunger, and a surface sensor assembly for use in a spiral plating apparatus. When the spiral has been completed, the plate is incubated and the resulting colonies are counted in a suitable area of the plate.