Apparent photosynthesis (APS), petiole nitrate-nitrogen concentration (petiole NO₃-N), and specific leaf weight (SLW) of three cotton: (Gossypium barbadense L.) and (G. hirsutum L.) genotypes, classified as normal and tip-clustering on sympodia basis, were evaluated for their responses to leaf aging under high and low planting density treatments at Tucson. Arizona in 1984 and 1985. In addition. The relationship among these characteristics and leaf age were determined. Combining data for all genotypes. Regression analysis showed that APS and petiole NO₃-N concentration decreased as a linear function of leaf age for all genotypes in both seasons. Except for DPL-90 SLW was not affected significantly by leaf age. APS and petiole NO₃-N were negatively correlated with leaf age. APS was positively correlated with petiole NO₃-N under both planting density treatments in both seasons. However, there was no correlation between leaf age. APS or petiole NO₃-N and SLW among the three genotypes under both planting density treatments in 1985. Planting density treatment had no effect on the aging pattern or on the association between these characteristics and leaf age a regardless of genotype or season.