In the report of the ICES/SCOR nutrient calibration, Koroleff and Palmork (1997) give a relative precision for phosphate of ± 15% at the low level (0.2 µmol/L), at the medium level (0.9 µmol/L) ± 5% and at the high level (2.8 µmol/L) ± 2%. at the Baltic Intercalibration Workshop (Kiel.1977) nearly identical results were obtained with natural samples having salinities of from 5 to 34. The Fifth ICES Intercomparison Exercise confirmed these results. Standard deviation of 0.03-0.09 µmol/L were found for phosphate concentrations up to 3 µmol/L. This is considerably higher than the reproducibility in the laboratory of 0.02-0.03 µmol/L