Centre for Add Zone Studies, U. C. N. W., Bangor, Gwynedd LL57 2UW, Wales, United Kingdom Manuscript received 21 April 1986, revised 3 September 1987, accepted 13 January 1988 THE Fiske- Subbarow method1 for the quantitative determination of inorganic phosphate suffers from the lack of stability of the blue colour of the reduced phosphomolybdate complex. The method was modified by Lindemann2 using a combination of hydrazine sulphate and stannous chloride, by Martland and Robison3 using quinols in sodium sulphate and by Ames5 using ascorbic acid as the reductant. Further modifications were carried out by Delory4 and King5 , and the latter has been successfully used by Khan and Rao6.