Two types of fluorimeter (inductíon and modulated) were employed to compare the intrinsic photosystem 2 efSciency of sun-exposed and shaded flag leaves of two cultivars (ICSV112 and Aralba) of sorghum, in the irrigated and unirrígated fleld plots at Monterotondo, Rome. Generally there was a good correlation between instruments, but for the irrigated sun adapted leaves of both cultivars much larger ratios were recorded with the modulated fluorimeter than with the inductíon one. This discrepancy was attributed to an insufficient flash intensity in the inductíon systém when measuring the healthy leaves adapted to a high irradiance.