New phenothiazine derivatives of general formula (I) in whichR represents 4- to 6-membered cycloalkyl, or represents --CH.sub.2 R" in which R" is hydrogen, alkyl containing 1 to 5 carbon atoms, alkenyl or alkynyl containing 2 to 4 carbon atoms, cycloalkyl (3- to 6-membered), phenyl, optionally substituted (with 1 or 2 halogen atoms or with a hydroxyl, alkyl, alkyloxy, trifluoromethyl or nitro radical) or heterocyclic selected from furyl, thienyl or pyridyl, andR' either represents a radical of general formula (IIa) in which R.sub.1 and R.sub.2, which may be identical or different, are alkyl, cycloalkylalkyl, hydroxyalkyl or acetyloxyalkyl or, together with the nitrogen atom to which they are attached, form a saturated or partially unsaturated 4- to 7-membered heterocycle optionally substituted with 1 or 2 alkyl, hydroxyalkyl or acetyloxyalkyl radicals, andR.sub.3 is phenethyl or alkyl optionally substituted with cycloalkyl (3 to 6 carbons) or benzoyl, or represents a radical of general formula (IIb) in which R.sub.1 and R.sub.2 are defined as above.The new products are useful as antispasmodics. ##STR1##