Data of blood and/or plasma constituents of three weeks old Japanesequail were used to predict the growth and some carcass traits of 6 weeks oldquail. Stepwise regression analysis was performed to partition the variability ingrowth and carcass traits of three lines of Japanese quail differing in geneticbackground. The first and second lines were selected over three generations forhigh six week-body weight (HBW6) and high 0-6 week growth rate (HGR0-6)respectively, whereas the third randombred control line (RC) was kept in orderto facilitate comparison among lines. The results cleared that the mostimportant predictor for live body weight at six weeks of age (LBW6) in bothmales of RC and males of HGR was thyroxine (T4). Both plasma total lipidsand total proteins (TL and TP) were the best predictors for LBW6 for femalesof RC line. Model 2 which used hemoglobin (Hb) and T4 was the best modelfor predicting LBW6 for males of HBW6. Whereas, TL was the most importantpredictor for LBW6 for females of HBW6 line. The most important predictorsfor feed conversion (FC) were TL and T4 for males of RC line, white and redblood cells (WBC and RBC) for females of RC, T4 and packed cell volume(PCV) for males of HGR0-6, triglycerides (TG) and TL for females of HGR0-6,TL and WBC for males of HBW6 and growth hormone (GH) and PCV forfemales of HBW6 line. Performance index (PI) was predicted through TL andalbumin (Alb) for males of RC, TP and GH for females of RC, T4 and PCV formales of HGR, TG and TP for females of HGR, TL and ratio oftriiodothyronine to thyroxine (T3/T4) for males of HBW6 and TG and T3/T4 forfemales of HBW6. For predicting dressing% in all studied groups, the mostimportant predictors were T3/T4 and TP for males of RC, TP and GH forfemales of RC, ratio of T3/T4 and T3 for males of HGR0-6, Alb and TP forfemales of HGR0-6, PCV and RBC for males of HBW6, Alb and T3/T4 forfemales of HBW6, respectively. Carcass% for all studied groups could bepredicted using these predictors: PCV and GH for males of RC, GH and TG forfemales of RC, GH and RBC for males of HGR0-6, WBC and T3 for females ofHGR0-6, T3/T4 and Hb for females of HBW6, respectively. The most importantpredictors for boneless meat% (BLM) were RBC and TP for males of RC, Hband Alb for females of RC, TG and T4 for males of HGR0-6, TP and T4 forfemales of HGR0-6, T3/T4 and Alb for males of HBW6 and TL and Hb forfemales of HBW6, respectively. The major predictor in determining protein%for both males and females of the HBW6 line was T3. The most importantpredictors for fat% were T3/T4, TL and TP in a descending order for males andfemales of the RC line and males of HBW6, respectively. The predicted traitswere insignificantly differed than the actual values or percentages(P>0.05). Therefore, results of the stepwise regression analyses revealed thateither certain studied hematological values or plasma constituents at threeweeks of age in studied lines of both sexes could be used to predict carcass andgrowth productive traits in Japanese quail with high precision and low error.