Basic azo dyestuffs, free from sulfo groups and having the formulaWherein Z is the radical of a tertiary amino group or of a quaternary ammonium group, Alk is alkylene of two to five carbon atoms, X is oxygen, Ar is phenylene unsubstituted or substituted by alkyl of one to four carbon atoms, alkoxy of one to four carbon atoms and/or chlorine or bromine, and K as the radical of a coupling component is the radical of a tertiary amine of the benzene series, the radical of 2,6-diamino-3-cyano-4-methyl pyridine or a derivative thereof or the radical of the 2-hydroxynaphthalene series, which are suitable for the preparation of writing and stamping inks or pastes for ball-point pens as well as suitable in offset printing and for the dyeing, printing or mass dyeing of, for example, tannined cellulose fibers, silk, hair, leather, acetate silk, polyamide fibers or acid modified polyolefins, polyamide or polyester fibers and fibers containing polyacrylonitrile or polyvinylidene cyanide. The dyeings obtained on these fibers have, in general, a high color intensity and, in general, good fastness to light and to wet processing. The dyestuffs can be used in slightly acid and strongly acid baths and are stable at a temperature above 100.degree.C as used in high-temperature dyeing. Wool is completely reserved by the dyestuffs under normal dyeing conditions.