Comparisons of chlorophyll and phaeophytin measurements performed on field and laboratory cultures of algae showed that fluorometric analyses were comparable to the standard spectrophotometric method over a wide range of phaeophytin, chlorophyll, and chlorophyll-b:chlorophyll-avalues. Inaccurate phaeophytin measurements obtained using a commercially available fluorometer were attributable to an incorrect narrow bandpass excitation filter which can now be replaced by the company. Differences in filtration and extraction technique and in frozen storage time did not result in significant changes in pigment estimates.