This paper critically surveys earlier definitions of the natural capital co
ncept and several preliminary attempts to measure it. Utilizing Georgescu-R
oegen's thoughts on funds, flows and stocks, I offer several (hopefully rig
orous) definitions of natural capital. I close by arguing that measurement
of ISEW, not of total natural capital, should be a priority of ecological e
conomists. (C) 1998 Elsevier Science B.V. All rights reserved.