Respiratory disorders cannowbeclassified by theaveragelaboratory asprimary defects of respiratory mechanics orofgasuptake, andthe verdict isaccepted withreasonable confidence. However, further classification ofdisordered gas uptake isstill a tedious anduncertain business. Theaimofpartitional respirometry istomeet thischallenge, distinguishing threebasic components ofthegasuptake process (effective deadspace,diffusing capacity, andpulmonary perfusion). Inconvenience to thepatient is minimal, since allthatisrequired isthebreathing ofa composite gasmixture containing verylow concentrations (300p.p.m.) of ether, carbon monoxide, andacetylene. Theuptake ofeach gasisdetermined byinfra-red analysis. Ether uptake isdependent mainly on ventilation and slightly onperfusion, carbon monoxide uptake on ventilation anddiffusion, andacetylene uptake on perfusion andventilation. A series ofsimultaneousequations withtermsin ventilation, diffusion, andperfusion areobtained, anditis thena simple mattertopartition thegasuptake process intothese three independent components. Thetechnique was originally introduced by HatchandCook(1955), andsomedatarelating to mine-workers werebriefly reported atthattime. Morerecently, simultaneous analysis ofthethree gasesandotherrefinements haveconsiderably increased theprecision of themethod, and multiple regression analyses whichpermit the prediction ofnormalvalues havebeencompleted (Shephard, 1958). Themainobject ofthepresent paperistoevaluate theusefulness ofpartitional respirometry ina variety ofpatients studied in some detailby conventional clinical and physiological methods.