A canine model was used to investigate the effects of intracarotid methylglucamine iothalamate (280 mgI/ml) at different viscosities on the normal blood-brain barrier. To alter viscosity, without changing physiochemical parameters, injections were made at either 23 degrees C or 37 degrees C. The degree of blood-brain barrier damage was assessed using Evans' Blue dye as a visual marker and by contrast enhancement measured by a computed tomographic (CT) scanner. It was found that methylglucamine iothalamate caused more blood-brain barrier damage at 23 degrees C than at 37 degrees C (p less than 0.1). Control studies at each temperature using intracarotid injections of physiological saline showed no temperature effect (p greater than 0.1). The implications of these findings are discussed.