Growth rate and the doubling time of Lin⁻ Rho^low/Ho^low cells incubated in the presence of medium containing IL-3, IL-6, IL-11, and SCF. Immediately after their purification, Lin⁻ Rho^low/Ho^low cells were suspended at 10 × 10³ cells/mL in medium containing 4 cytokines and incubated at 37°C in a 5% CO₂ containing humidified incubator as described in the Materials and Methods. At indicated intervals, duplicate aliquots of cells from growing culture were counted using a hemocytometer. The numbers in the parentheses of the insert indicate the number of experiments from which the values for that particular time point were obtained.