Polyamine biosynthesis and arginase activity in psoriasis were studied using keratotome strips and suction blister roofs as specimens. In the uninvolved psoriatic skin a slight (1.3-fold; p less than 0.05) increase in the spermidine level was observed compared with control skin. There was also a 1.2-fold increase (p less than 0.05) in the spermidine/spermine molar ratio, which is considered to be an indicator of proliferation activity. No changes were noted in other polyamines or polyamine-synthesizing enzymes ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (AMDC) in the uninvolved psoriatic skin vs. control skin. Neither was there any significant difference in the arginase activity. In psoriatic lesions the levels of all polyamines, as well as the activities of biosynthetic enzymes, were significantly (p less than 0.001) elevated. The putrescine level was elevated to 2.5-fold, spermidine to 2.7-fold and spermine to 1.4-fold. The enzyme activities expressed severalfold increases. The enhancement of arginase activity was less prominent than that of polyamine-synthesizing enzymes, but the increase from 271 +/- 88 to 354 +/- 126 mumol/g/h (1.3-fold) was statistically significant (p less than 0.001; paired t-test). The increase in arginase activity in suction blister roofs, which represents pure epidermis, was more pronounced than that in keratotome strips, i.e. about double. The results show thus that polyamine biosynthesis is significantly enhanced in psoriatic lesions, but there is only a slight difference between the uninvolved psoriatic skin and control skin.(ABSTRACT TRUNCATED AT 250 WORDS)