This accelerator mass spectrometry (AMS) system shows a one-to-one relationship between sample carbon-14 concentrations determined by AMS and by beta-counting. Measurements of unknown samples against a standard indicate that carbon-14 concentration measurements to better than two percent can be made. For a 30-second data collection interval in a typical run of 100 intervals, the variability of the beam injected into the accelerator is about two percent, that of the machine transmission is about four percent, and counting statistics give 4.7% standard deviation for a sample of 80% of modern carbon. -- AATA