Compounds of formula I, wherein one of R.sub.1 and R.sub.2 is thienyl which is substituted by halogen and the other of R.sub.1 and R.sub.2 is substituted phenyl, wherein the substituents are as defined in the claims, with the proviso that the phenyl group is substituted by at least a cyano, carboxy or (.sub.C1-4)alkyloxycarbonyl group, are inhibitors of CCR9 activity and useful for therapeutic treatment.