Erythromycin derivs. of formula (I) and their acid addn. salts, are new. R = -(CH2)nAr; n = 3 - 5; Ar = heterocyclic gp. (opt. substd. one or more times) (37 gps shown in specification); or R = a gp. (i); Z = H or an acid residue. Ar can also be a gp. (a)-(e) (opt. substd.); R can also be a gp. (ii) or (iii); (opt. substd.). Also claimed are amines RNH2 (III) and their acid addn. salts.