Substituted alkadienes of formula: ##STR1## in which R.sub.1 is hydroxy or acetoxy, R.sub.2 is hydrogen, carboxy, alkoxycarbonyl, phenyl or benzoyl, andR.sub.3 is alkylthio or alkoxy and R.sub.4 is naphthoyl or optionally substituted benzoyl,or R.sub.3 is alkoxycarbonyl, cycloalkyloxycarbonyl or cyano and R.sub.4 is alkyl, naphthyl, optionally substituted phenyl, alkylthio, naphthylmethanethio, optionally substituted benzylthio, optionally substituted phenylthio, naphthylthio, phenethylthio or allylthio,or R.sub.3 and R.sub.4 form, with the carbon atom to which they are attached, a ring-system of formula: ##STR2## in which R.sub.5 is hydrogen or alkoxy and X is methylene or S inhibit 5-lipoxygenase and are useful, for example, as anti-inflammatories.