At the La Platina Experiment Station (INIA), several hundreds of bread and durum wheats lines were studied annually in yield trials under irrigation, between 1971 and 1981. In this paper, the effects of date of sowing, BYDV, aphids, accumulated degree-days (base 5ºC), and amount of ram on bread and durum wheats are analyzed. The average yields Jor the 11 years were 53.54 quintals/ha, for bread wheats, and 53.29 quintals/ha, for durum wheats. In years with early sowing dates, bread wheats produced 3.9 quintals/ha more; but in years with late sowing dates, durum wheats produced 2.8 quintals/ha more than bread wheats. In warmeryears, bread wheats yielded 1.9 quintals/ha more; but in cooleryears, durum wheats yielded 1.1 quintals/ha more than bread wheats. ln rainy years, durum wheats produced 2.4 quintals/ha more; but in dry years, bread wheats yielded 2.5 quintals/ha more than durum wheats. However, this last difference could be due to the fact that in rainy years sowings were done at later dates, which are favorable to durum wheats. No differences were detected due to the effect of BYDV or aphids on the comparative yields of the two types of wheats.