At the La Platina Experiment Station (INIA), several hundreds of bread wheat lines were studied ennually in yield trials, under irrigation, between 1971 and 1981. In this paper, the factors that influenced hectoliter weight, and Puccinia graminis, BYDV, and aphid infections are analyzed. Results indicated that the main factors affecting hectoliter weight were BYDV and commulative degree-days (base 5º C). Rainfail, P. graminis, aphids, and date of sowing did not affect hectoliter weight. Commulative degree-days and date of sowing affected the level of P graminis infection; but rainfali had no influence on this infection. BYDV infection was not affected by date of sowing, commulative degree-days orrainfall. The level of aphids infestation was affected by commulative degree-days and rainfall, but as not affected by date of sowing.