Nyctometry was used to assess macular recovery function in 234 diabetic patients; their retinopathy ranged from no retinopathy (99) to early background retinopathy (135). None had visual symptoms or macular oedema. Abnormal (reduced) nyctometry findings were significantly and directly related to the deterioration of diabetic retinopathy. There was no significant association between reduced or normal nyctometry findings and glycaemia at the time of the examination. The value of nyctometry in screening and follow-up is discussed.