Kocatepe, M.2016-02-082016-02-0819910025-2611http://hdl.handle.net/11693/26163In this note we study the relationship between the vanishing of Ext1(λ(A), λ(A)) and the existence of a regular basis in the Köthe space λ(A). We construct an example of a nuclear Köthe space λ(A) with no regular basis and such that Ext1(λ(A), λ(A))=0. Then we show that for some classes of Köthe spaces λ(A), the vanishing of Ext1(λ(A), λ(A)) yields a regular basis for λ(A). © 1991 Springer-Verlag.EnglishArticle10.1007/BF02568397