Estimating the growth response of Douglas-fir [ Pseudotsuga menziesii (Mirb.)] stands after nitrogen (N) fertilization is difficult due to high site variability in the Pacific Northwest. Our objective was to determine how site and soil variables influence stand response to applications of 224 kg N ha^-1 as urea once every four years. The unstandardized residuals of two dependent variables, total volume and 4-year periodic annual increment (PAI) were regressed against site and soil variables using stepwise regression techniques. Data were stratified by three different density management regimes (DMR): ISPHA (initial stems per hectare), ISPHA/2, and ISPHA/4. Total volume and 4-year PAI after two applications of urea was significantly higher (p < 0.01) in fertilized plots than non-fertilized plots. Only total volume was significant (p < 0.05) after the third fertilizer application, while PAI was not. Thinning effects were highly significant (p < 0.01) for all three fertilizer applications. The strongest related soil and stand variable to fertilization response existed between NH4⁺_(15-30cm) and 4-year PAI (adj. R² = 0.622) for the ISPHA/2 DMR, and relative density (RD) and total volume (adj. R² = 0.712) for the ISPHA/4 DMR. The best fit equation resulted from stratifying the data by the ISPHA/4 DMR (adj. R² = 0.822), which included RD, %C_(0-15cm), NH4⁺_(30-50cm) and elevation. The most influential variable in highly correlated multiple regression equations was RD. Our results demonstrate that multiple applications of urea provide significant increases in total volume but fertilization effects diminish over time.