Little is known about the nitrogen (N) nutrition of the cotton (Gossypium hirsutum L.) crop during the latter part of the season. Therefore, a 3-year field study was conducted in Marianna, Arkansas, to determine the end-of-season N requirement, effect of N on canopy photosynthesis, effect of leaf age on 15N uptake, and the value of late-season foliar-N applications on boll development and yield. In 1990, three foliar treatments were applied consisting of: (1) a single spray, (2) two sprays, and (3) three sprays during the first three weeks of August. In 1991 and 1992, the soil N level was divided into low and high N levels of approximately 80 and 110 lbs N/acre and the same foliar treatments were applied at the growth stages of nodes above the uppermost white flower = 7, 6, and 5. The nodes above white flower count and the yield were significantly increased over the control whereas no significant differences were found within the three different foliar sprays. For the leaf age study, four different leaf age groups viz: 10, 20, 40, and 60 d-old mainstem leaves were selected at the mainstem node-10 position. Maximum (15)N uptake was recorded by the 20 d-old leaf which was also the most photosynthetically active leaf. As the leaf aged, the uptake declined with concomitant translocation of most of the absorbed N to the lint and seed, indicating these as the major sinks. (15)N uptake and canopy photosynthesis were measured under 4 different soil N levels viz: 0, 50, 75, and 100 lbs N/acre. As the season progressed, canopy photosynthesis decreased drastically in the 0, 50, and 75 lbs N/acre soil levels compared with the 100 lbs N/acre soil level. (15)N uptake data showed that the middle positioned bolls in the canopy had the maximum uptake, whereas no significant differences were found between the top and bottom bolls. There was significant yield differences between the four soil N levels.