The suitability of the Hach method for protein nitrogen estimation was determined for the analysis of periphyton samples. Preliminary laboratory tests suggest that the Hach method gives substantially higher total nitrogen recoveries from periphyton than traditional Kjeldahl methods. On the basis of incomplete nitrogen recovery the suitability of traditional Kjeldahl methods to the analysis of periphyton is questioned. For the analysis of relatively indigestible periphyton 30% hydrogen peroxide was not found to be a suitable reagent.