Pre-harvest prediction of winter wheat (Triticum aestivum L.) grain yield and/or protein could assist farmers in generating yield maps and reliable product marketing. This study was conducted to determine the relationship between spectral measurements (taken from Feekes growth stage 8 to physiological maturity) and grain yield and grain protein. Spectral measurements were taken using photodiode detectors and interference filters for near-infrared (NIR) and red spectral bands. The study was conducted over 2 years at seven locations where existing field experiments were already in place across Oklahoma. Spectral readings were taken at Feekes growth stages 8, 9, 10.5, 11.2, and 11.4. The normalized difference vegetative index (NDVI) was calculated. In both cropping cycles, NDVI was well correlated with grain yield, grain N uptake, straw N uptake, and total N uptake at Feekes growth stages 9 and 10.5 (R2>0.5). However, by Feekes 11.2 no relationship between NDVI and grain yield or N uptake was observed. In 19...