We prove the following theorems:
(1) If X has strong measure zero and if Y has strong first category, then their algebraic sum has property S0.
(2) If X has Hurewicz's covering property, then it has strong measure zero if, and only if, its algebraic sum with any first category set is a first category set.
(3) If X has strong measure zero and Hurewicz's covering property then its algebraic sum with any set in is a set in . ( is included in the class of sets always of first category, and includes the class of strong first category sets.)
These results extend: Fremlin and Miller's theorem that strong measure zero sets having Hurewicz's property have Rothberger's property, Galvin and Miller's theorem that the algebraic sum of a set with the γ-property and of a first category set is a first category set, and Bartoszyfński and Judah's characterization of -sets. They also characterize the property (*) introduced by Gerlits and Nagy in terms of older concepts.