A sample with a carbon-14 concentration estimated to be greater than 30, 000 Modern was inadvertantly graphitized and measured in an accelerator mass spectrometry (AMS) system. No measurable contamination of the cesium sputter ion source was observed. Simple cleaning procedures removed the contamination from the sample preparation system, with the exception of the reaction vessel in which the sample was graphitized. Sample cross-contamination factors were estimated for all of the preparation and measurement procedures.