There is disclosed the use of a compound of formula (I), wherein R¹, R², X, Y, V, W and Z are as defined in the specification, and pharmaceutically acceptable salts, enantiomers or racemates thereof, in the manufacture of a medicament, for the treatment or prophylaxis of diseases or conditions in which inhibition of nitric oxide synthase activity is beneficial. Certain novel compounds of formula (Ia) and pharmaceutically acceptable salts thereof, and enantiomers and racemates thereof are disclosed; together with processes for their preparation, compositions containing them and their use in therapy. The compounds of formulae (I) and (Ia) are inhibitors of the enzyme nitric oxide synthase and are thereby particularly useful in the treatment or prohylaxis of inflammatory disease ##STR1##