Improvement of yield in maize by breeding has generally resulted in narrowing genetic basis of breeding populations and in decreasing genetic diversity between hybrids in commercial production. Besides, only few heterotic patterns have been used in developing new hybrids. Local (exotic) maize germplasm might be useful for broadening the genetic basis of breeding populations and for developing new heterotic patterns. Conventional studying genetic variability of the germplasm could be complemented with the biotechnological approach. Nine inbred lines, FAO 300-400, developed from local open pollinated cultivars were crossed to a tester from the BSSS heterotic pool and to a tester from the Lancaster heterotic pool each. The obtained hybrids along with a commercial hybrid - control were evaluated in field experiment at two locations during two years. The test hybrids were compared in grain yield, percent of kernel moisture, lodging, ear length and 1000 kernel weight to the control and among themselves. Also, the lines and the testers were analysed for 13 enzymatic systems at 23 loci by using starch gel electrophoresis. The test hybrids compared favourably in grain yield and several other traits with the control. However, in resistance to lodging the hybrids were generally worse than the control. The half-sib hybrids, i.e. hybrids of a line with two testers, were similar in the analysed traits to each other, except for one inbred line which showed higher level of absolute heterosis crossed to the BSSS tester. The obtained results from electrophoretic analysis complement the results obtained in the field experiments well. Eight inbreds had nearly equal number of different alleles per locus at four to eight loci, out of 23 loci analysed, compared to both testers. The line which showed different heterosis with the two testers had more different loci compared to the BSSS tester than compared to the Lancaster tester. In the studied inbred lines several alleles were found, i.e. Acp1-6, Got2-2, Idh1-6, Pgd2-2.8, Aco1-1, Glu1-2, which some authors (Stuber and Goodman, 1983) reported as the rare ones. The studied maize inbred lines might be useful germplasm for broadening the genetic basis for yield of breeding populations of both BSSS and Lancaster heterotic pool. Also, they could be used for development of breeding source populations representing and independent heterotic pool. In both cases care should be taken of genetic basis for stalk standability. The isoenzymatic analysis could complement the field quantitative trait (i.e. yield) results in regard to genetic variability and heterotic pattern.