A semiautomatic nondispersive infrared analyzer apparatus has been developed for analysis of up to 50 CO2 air samples per day. The samples are collected in 500-ml glass flasks and are transferred to the analyzer with a novel, free-floating piston-pump. Sample and calibration gas transfer operation are controlled by a microprocessor, and data are recorded, analyzed, and output by a Hewlett--Packard 9845A/S desktop computer. The apparatus is described, including operating and test modes, and performance characteristics determined from 2 years of operation are given.