The present work was undertaken to study the effects of a deproteinized extract of calves' blood (Solcoseryl) on developing granulation tissue in rats. Cylindrical hollow viscose cellulose sponge implants were used as an inductive matrix for the growth of granulation tissue. In the first, sham group the implants were treated daily by withdrawing 1 ml of wound fluid from the central dead space of the implant and then re-injecting the fluid. In the second, experimental group the aspirated wound fluid was replaced by a corresponding volume or Solcoseryl. Analyses of wound fluid and granulation tissue were carried out 4, 10 and 21 days after implantation. A statistically significant increase of granulation tissue hemoglobin (+21%) was observed at 10 days in the Solcoseryl group as compared with the sham-treated rats, indicating an enhanced capillary ingrowth. Concurrently, the mean amount of DNA in the Solcoseryl-treated tissues was elevated by 48% over the level of the sham-treated group, demonstrating an augmented cellularity of granulation tissue. At 21 days the mean amount of collagen hydroxyproline of the Solcoseryl group was 31% above the level measured in the sham-treated animals. PO2, PCO2 and pH in the wound fluid and the amounts of RNA and uronic acids showed no essential differences between the two groups. These data demonstrate a stimulatory effect of Solcoseryl on several aspects of granulation tissue formation: augmented vascularization, elevated cellularity and subsequent enhancement in the accumulation of collagen.