The Bureau of Mines has developed a trace helium analyzer for determining helium-4 in the parts-per-billion range. The instrument is used for analyzing pure gases, laboratory-prepared standards, and atmospheric samples. Accuracy at the 95-pct confidence level in the 50- to 20,000-ppb range is within +/-2 ppb or +/-0.4 pct, whichever is greater. The minimum detectable helium-4 concentration is calculated to be 5 ppb. The analyzer consists of a modified helium leak-detector mass spectrometer, a laboratory-built sample inlet system, and a liquid-nitrogen-cooled charcoal trap. A programmable integrator and event-control module make automatic operation possible. The portability of the analyzer allows it to be used in the field.