Active radiometers have been tested extensively as tools to assess in-season nitrogen (N) status of crops like wheat (Triticum aestivum), corn (Zea mays), and cotton (Gossypium hirsutum).  Fewer studies target in-season plant growth parameters such as biomass, plant height or leaf area index (LAI).  Uses of this plant data include simulation modeling, total N uptake measurements, evapotranspiration (ET) estimates and irrigation recommendations.  Our objective in this study was to examine relations between canopy reflectance and biomass, LAI and plant height in irrigated cotton.  Canopy reflectance was measured at 1 m height above the tallest plants in field using two, three-band Crop Circle ACS-470 radiometers in a 2.5-ha irrigated nitrogen (N) fertilizer management study in cotton in central Arizona. Cotton was planted in May in 1 m rows.  There were 18 plots that were 170 m long.  Interference filters were centered on 800, 780, 730, 670, 590, and 530 nm.  Wavelength widths were 20 nm for 800 and 780 nm and 10 nm for the rest. Plant height was estimated with a Honeywell 943 ultrasonic distance sensor.  Canopy reflectance and plant height were sensed every 7 to 14 days during the season with one pass per plot at 0.5 m/sec, and data were acquired at 5 Hz. Leaf area index was measured five times per season at 24 to 72 DGPS-referenced points using a Li-Cor LAI-2000 Plant Canopy Analyzer.  Manual plant heights were taken at the 72 points as well.  Biomass (1 m²) samples were cut at ground level two times during the season.  Variation in plant parameters were due to N fertilizer treatments and to sandy areas of the field with reduced water holding capacity.  Several vegetative indices (VIs) were calculated and correlated with biomass, LAI, and plant height.  Correlations were strongest with VIs and LAI or plant height and weakest with biomass. The normalized vegetative index (NDVI) using red as the visible band correlated with LAI, biomass, and lint yield better than using green or amber. NDVI amber correlated with N rate slightly better than NDVI-red.  Correlations were weaker from using VIs that used reflectance in the red edge such as normalized difference red edge (NDRE) or the DATT index.   In summary, NDVI calculated with and active sensor and plant height from an ultrasonic sensor appear to have potential to guide N fertilizer management, plant growth regulators and or harvest aid applications in irrigated cotton in the southwest USA.