99mTc-HSA-MM proved to be a valuable agent for both bone marrow visualisation and exploration of the phagocytic and proteolytic function of the RES-macrophages in psoriatic patients. 24 psoriatics and 24 normal healthy adults were examined. 18 (75%) of the psoriatics studied demonstrated peripheral extension of the bone marrow space, whereas this phenomenon could not be observed in normal subjects. The phagocytic and proteolytic turnover of 99mTc HSA-MM in liver, spleen and bone marrow was found to be accelerated in 66% (n = 12) of the systemically untreated persons. Six psoriatics treated systemically with aromatic retinoid for a longer period showed 2x a delayed and 4x a normal turnover; three patients with cirrhosis of liver showed in each case a delayed turnover of HSA-MM - Human Serum Albumin-Millimicrospheres.