The photosynthetic and transpiration rates of various cultivars of pigeon pea (Cajanus cejen (L.) Millsp.) were measured using a portable infrared gas analyzer system at the Fortuna Experimental Station in Puerto Rico. The 16 lines studies were long-day determinate types and showed great variability at 4.5 months after planting with respect to plant height (0.8S-2.lm), photosynthetic rate (0.19 - O.8Smg C02 m-2 sec.r l) and transpiration rate (263 SS6mg "20 m-2 sec.-1). Conductances also varied over a 3-fold range. Leaf nitrogen and chlorophyll were also measured for correlation with photosynthesis. The 16 lines have been shown to have distinct physiological attributes. ----- La tasa fotosintefica y de transpiracioh de varias variedades de gandril (Cajanus ceisn (L.) Millsp.) fueron medidas, usando un sistema portatit de analisis infrarojo de gas, 10 cual se llevo a cabo en la Estacidn Experimental La Fortuna en Puerto Rico. Las dieciseis variedades que fueron estudiadas eran de tipo determinado y de dfa largo y rnostraron gran variabilidad. a los cuarenta y cinco dias despues de haber sido plantadas, en 10 referente a: la altura de la planta (0.85-2.1 rn), tasa fotosintetica (0.19-0.8Smg C0 2/m2 /sec), tasa de transpiracion (263-5S6mg "20/ m2/sec). La conductancia tarnbien vario"en una escala mayor de tres veces, La cantidad de nitrogeno y de clorofila tarnbien fueron medidas para poder correlacionarlas con la fotosintesis. La dieciseis variedades mostratdn tener atributos fisiol6gicos diferentes.