The resistance of maize inbred lines and their hybrids to Western Corn Rootworm was investigated in a 4 × 4 full diallel system. The most tolerant line against WCR larvae was the inbred line P26. Four maize inbred lines and their 12 normal and reciprocal crosses were investigated for resistance to Fusarium ssp. and European Corn Borer under natural conditions in four replications in 1998-2000. The highest GCA values were found for the inbred lines P26 and P50. Studies were also made to determine the optimum concentration of imidazolinone in the selective medium for the detection of resistant cell lines originating from homozygous genotypes produced by irradiation.