Plasma albumin, plasma volume and the transcapillary escape rate of albumin (TERalb), i.e. the fraction of the intravascular mass of albumin that passes to the extravascular space per unit time, were determined using 125I-labelled albumin in 26 patients with varying degrees of psoriasis. For the patients as a group the plasma albumin concentration and the TERalb values were not significantly different from the control group. This contrasts with earlier findings in erythrodermic patients. The plasma volume was significantly reduced whether it was expressed in relation to body weight, height or surface area (P less than 0.001). Thus the intravascular mass of albumin (IVM), determined as the product of the plasma volume and the plasma albumin concentration, was also significantly reduced (P less than 0.001). We found no correlation between the involved skin area and any of the above mentioned parameters. The possible mechanisms in the reduction of the plasma volume and the IVM are discussed. It is suggested that reduced IVM may reflect reduced total albumin mass due to lowered rates of albumin synthesis or increased rates of turnover.