This paper is concerned with the stability of certain properties of linear operators in locally convex topological vector spaces under perturbations by operators which aresmallin some sense. Section 3 deals with the very useful concept of Banach balls which was introduced by Raĭkov [9]. Some properties are discussed. The following section investigates the invertibility of certain operators generalizing results of Robert [10] and de Bruyn [2],[3]. These results are used extensively in the sequel. We go on to discuss Riesz operators. We obtain results stronger than those of de Bruyn [1] with regard to asymptotically quasi-compact operators in locally convex spaces. The proofs are basically adaptations of those from [1]. In the final section we observe some results concerning the range ad null space of an operator perturbed byboundedoperators. We obtain a result very similar to an unproved theorem of Vladimirskiĭ [a] and point out their differences. MOS codes 4601, 4710, 4745, 4768, 4755.