Abstract: This invention relates to an apparatus and method for streaking a sample on a Petri plate. The objective is to provide a method and apparatus in which the inoculum is sequentially streaked in a series of dilutions in a manner closely simulating previous manual practice but with a consistency, safety and accuracy which is not manually achieved. A sequential series of spreader heads are brought into contact with the culture medium on a Petri plate and swept back and forth over the medium surface to streak the inoculated sample in a segment of the plate. The paths of the second and subsequent spreading heads are angularly displaced from the path of the preceding spreading head, so that the segment of the plate in which the second and subsequent spreading heads streak the sample will partially overlap the respective preceding segment. This is best achieved by oscillating the support of the Petri plate and sequentially moving a spreading head radially during such oscillation.