From plasmodia of the slime mould Physarum polycephalum a yellow pigment physarochrome A (1) has been obtained. Its structure has been established as all-trans N-[ll-~2-acetylamino-3-hydroxyphenyl)-2,4,6,8,1O-undecapentaenoyl]-S-glutami(l) ij;, the basis of spectroscopic evidence and hydrogenation to a decahydro derivative.