We used active fluorescence techniques (fast repetition rate and pump- during-probe fluorometry) and flow cytometry to characterize the phytoplankton in depth profiles and surface transects during the late summers of 1997 and 1998 in the Ross Sea and the Polar Front, respectively, as part of the USJGOFS Southern Ocean program. During a transect across the Polar Front, we observed the highest relative variable fluorescence values near the Front (60-62 S). In a transect along 76.5 S in the Ross Sea, the highest relative variable fluorescence was observed at a near-shore station in pack ice; the other stations all were much lower in variable fluorescence. Individual cell measurements indicated that the active fluorescence characteristics of most phytoplankton groups in a given water sample were similar, with the exception of cryptophytes, which always had higher variable fluorescence than other cells. Flow cytometric measurements of light scattering and fluorescence indicated that cryptophytes, though present at most stations, never accounted for more than 10 percent of estimated phytoplankton carbon. Pennate diatoms likewise were never major constituents of the phytoplankton crop and were abundant at only a few stations. Mean relative variable fluorescence of near-surface cells was inversely correlated with mean cell volume, and to a lesser extent with total phytoplankton carbon. Relationships between phytoplankton characteristics and environmental parameters (including iron concentrations) will also be discussed.