The modified Abel lemma on summation by parts is employed to investigate the partial sum of Dougall's 5 H 5 -series. Several unusual transformation formulae into fast convergent series are established. They lead surprisingly to numerous infinite series identities involving π, ζ(3) and the Catalan constant, including several important ones discovered by Ramanujan (1914) and recently by Guillera.License or copyright restrictions may apply to redistribution; see http://www.ams.org/journal-terms-of-use 476 WENCHANG CHU AND WENLONG ZHANGfor convergence. This is not an isolated case. In fact, all 31 principal series for 1/π and 1/π 2 , including Bauer's, collected by Glaisher [32] can be derived from this formula published by Dougall [31] in 1907, two years after Glaisher's paper. Following the same approach of Bauer, Levrie [45] recently derived two further infinite series expressions for 1/π and 1/π 2 ; but both of them result again from special cases of Dougall's summation theorem. Wilf and Zeilberger [53] introduced a new and powerful method, based on Gosper's indefinite summation algorithm [33], for proving identities for hypergeometric series (cf. Petkovšek, Wilf and Zeilberger [46] also). This approach has further been developed intensively by Guillera [39], who reviewed systematically the formulae discovered by Ramanujan [49], found further π-formulae of Ramanujantype and conjectured experimentally the following beautiful and challenging series