A chemically synthesized gene encoding human CuZn superoxide disute (hSOD) was loned into the shuttle vector pBAX18R and expressed in Anacysts ins 6301 (Synechococcus sp. strain PCC 6301) under the control of a ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbc) promoter derived from A. nidulans 6301. The sequences immediately upstream from the hSOD coding region and the distances between the ribosomal binding site and ATG initiation codon strongly affected the expression of the hSOD gene in A. nidulans cells. Optimal expression of hSOD was obtained with the expression vector pBAXSOD8-I, which contained a GGAGAG sequence. In defined conditions, irradiation with light increased hSOD enzyme activity in the transformants >18-fold and the level of the hSOD protein reached a value of about 3% of the total soluble protein. The trnsformants that expressed hSOD acquired the ability to extenuate photooxidative damage induced by methyl viologen.