ズウォティ
The IV series banknotes had a longer life. Mainly due to their underdeveloped security features, the first three series were taken out of circulation in line with legislation signed on 28 October 1950, covering the introduction of the new Polish złoty (PLZ). Older banknotes had to be exchanged within 8 days for the new series IV, which had been designed, printed and distributed in great secrecy.