Some level of cellular or tissue differentiation is needed for the biosynthesis of many important compounds in plant cell cultures. The culture of compact callus aggregates (CCA) consisting of spherical, smooth-surfaced clumps of 2-7 mm in diameter displaying some level of cellular and tissue differentiation was initiated from the stems of R. sachalinensis. Histochemical analysis showed that the CCA were structurally organized to facilitate nutrient transport. The kinetics for CCA growth and salidroside synthesis were measured in shake flasks. it was found that a short phase of exponential growth (mu = 0.137 day(-1)) and a relatively long phase of linear growth (growth rate = 0.60 g day(-1) l(-1) predominated over most of the the culture cycle. The salidroside yield of CCA after 24 days of culture was 0.68% on a dry weight basis, approximately six times as much as that of the dispersed cells; however, the growth rate of CCA was comparable to that of the dispersed cells. The CCA suspension culture was also successfully carried out ill a 5-l airlift bioreactor. The yield of salidroside was similar to that of shake-flask cultures though the biomass was relatively small. No foam buildup occurred in the reactor Since rite medium remained almost clear throughout the culture cycle.