Mycelial soluble proteins of Pholiota nameko labeled in vivo during the Pi-supplied (P+) and the Pi-depleted (P-) cultures were separated by SDS-polyacrylamide gel electrophoresis and two-dimensional polyacrylamide gel electrophoresis, and visualized by fluorography. A comparison of protein profiles from the P+ and P- cultures showed that Pi deficiency induces the synthesis of 15 polypeptides and an increase in the relative amount of 29 polypeptides. These result suggests that many proteins may be specifically synthesized de novo under Pi deficiency as part of the adaptive mechanism for this condition.