Neurologically-active heterocyclic compounds comprising two fused 6-membered rings with nitrogen atoms at positions 1 and 3, a carboxy group at position 4, and a hydroxy group at position 8, with one ring being aromatic. Processes for the preparation of these compounds and their use as pharmaceutical or veterinary agents, in particular for the treatment of neurological conditions, and more specifically neurodegenerative conditions such as Alzheimer's disease.