The construction of eight nonisomorphic new symmetric (100,45,20)-designs, having E25 . S3 as their full automorphism group, is presented. 1. PRELIMINARIES Symmetric (100,45,20)-designs belong to Menon series consisting of all symmetric designs with parameters (4t2, 2t2 t, t2 t). The existence of such a design, on the basis of its equivalence with the existence of regular Hadamard matrix of ord...