The characterization of S-implications generated from strong negations presented firstly by Trillas and Valverde in 1985 is wellknown in the literature. In this paper we show that some assumptions are needless and present two characterizations of S-implications with mutually independent requirements. We also present characterizations of (S, N)-implications obtained from continuous fuzzy negations or strict negations. Besides these main results some new facts concerning fuzzy implications, fuzzy negations and laws of contraposition are proved. © 2007 Elsevier B.V. All rights reserved.