A molecular sieve (Type 3A) drier system was installed on PDU P-99 for confirmatory testing. During 70 h of continuous operation, three drying and two regeneration cycles were completed. The drier processed bleed off-gas at unit pressure and ambient temperature in tandem with the butane scrubber. High pressure hydrogen was used to regenerate the molecular sieve adsorbent at 500/sup 0/F. Although the tests should be considered preliminary because of uncertainties in the moisture and gas rate measurements, the results were in good agreement with the predicted performance, and the apparatus operated with minimum difficulty.