In 30 patients affected by Porphyria Cutanea Tarda we determined: plasmatic, erythrocytary and urinary zinc (by atomic absorption spectrophotometry); total porphyrins in plasma and in urines, coproporphyrins and protoporphyrins in erythrocytes (by spectrophotometric methods); haptoglobin, hemopexin, alpha 2-macroglobulin and albumin (by immunological methods). The results obtained were compared with those of normal subjects. In addition, the variables under consideration were statistically analyzed to bring out possible correlations (both simple and partial). The most interesting result (besides the documentation of an increase in the urinary and plasmatic zinc in porphyric patients) was the finding of correlations between plasmatic zinc, plasmatic porphyrins and alpha 2-macroglobulin.