A simplified chlorophyll analytical procedure is described that requires 4 min/sample and features an overall precision (measured by the coefficient of variation, C.V.) of ~ 3% at the 15 mg/m3 chlorophyll a level. The C.V. varies inversely with concentration for spectrophotometric determinations. The molar extinction coefficients (665 nm) for chlorophyll a were estimated to be 2.5–6.0% greater in acetone (90%) compared to methanol (100%) and 2.5% greater in a 1:1 mixture (v/v) of methanol-dimethyl formamide compared to methanol. Acetone (90%) extractions of naturally occurring mixtures of the common bloom-forming blue-green algae Microcystis, Oscillatoria, Aphanizomenon, and Anabaena yielded erratic recoveries of chlorophyll a. The lowest recovery (34%) occurred with an Oscillatoria population. On the one occasion when a four-way solvent extraction comparison was performed, acetone (90%) failed to extract 29 ± 2% of the chlorophyll a in a mixture of Anabaena, Microcystis, and Aphanizomenon, whereas the other three solvent preparations yielded identical (complete) extractions. Methanol or acetone-dimethyl sulfoxide are recommended for chlorophyll extraction from blue-green algae, while acetone-dimethyl sulfoxide is recommended for diatoms or Chlorophyta populations. Key words: chlorophyll, Cyanophyta, Chlorophyta, chlorophyll analysis, methanol, acetone, methanol-dimethyl formamide, acetone-dimethyl sulfoxide