The grain with ventral swelling (GVS) is regarded as one of the damaged grains in malting barley and it lowers the quality of grain. For the breeding of GVS-resistant lines, we investigated the environmental factors causing GVS occurrence for nine years from 1989 to 1997 using four barley cultivars. GVS occurred frequently in four years; 1990, 1994, 1996 and 1997, when the frequency was significantly different (P<0.01) among four cultivars (Table 1). A positive correlation was found between the percentage of GVS and the number of days with precipitation over 25 mm during a period of 15 days before maturity (Fig. 2, Table 2), and GVS occurred frequently in years with more than one day of the critical level of precipitation. In the test of covering the barley's spikes with paraffin paperbags to prevent rain during its maturity in 1998, the rainfall from 8 to 6 days before maturity caused GVS occurrence, but that from 4 to 2 days before maturity did not (Table 3). These results indicated that GVS occurrence was caused by successive rainfall and once GVS occurred on the spikes, it did not increase further. Thus, it was suggested that GVS resistance could be selected by applying successive artificial rainfall from the middle of the ripening stage of the early maturing cultivars to the ripening date of the late maturing cultivars.