Structure and distribution of the foliar epidermal hairs of 109 species and two varieties belonging to 39 genera of the family Acanthaceae have been studied. Both glandular and non-glandular epidermal hairs have been recorded in the investigated taxa. The glandular hairs may be subsessile or long-stalked. The subsessile glandular hairs are of two types: i) Glandular head panduriform, 2-celled, and ii) Glandular head globular or disc-shaped, 2—8- or more-celled. Subfamilies Nelsonioideae and Thunbergioideae are characteri«*H hv thfi nanduriform hairs, while Mendoncioideae and Acanthoideae have glandular hairs with a globular head. Long-stalked glandular hairs are present only in nine species. Non-glandular hairs are also widely distributed in the family; they are present in all but ten species. They may be unicellular, or multicellular uniseriate; rarely they are branched. Though the non-glandular hairs are of diagnostic importance at species level only, in some genera like Barleria, Ruttya, , and Äphelandra, they are quite characteristic. The present study does not support Bremekamp's (1965) delimitation of the family Acanthaceae, involving the transfer of Lindau's (1895) subfamily Nelsonioideae to Scrophulariaceae, and the raising of his subfamilies Thunbergioideae and Mendoncioideae to the rank of independent families. Instead, the retention of Nelsonioideae, Thunbergioideae, Mendoncioideae, and Acanthoideae within the family Acanthaceae is favoured.