Plantago major (Plantaginaceae) is popularly used to treat tumors, infections and as a blood purifier. Aqueous, methanol, chloroform and hexane extracts of the aerial parts (leaves and seeds) were added to CD(1) mice bone marrow and spleen cultures incubated at 37 degrees C for 72h, and also added to Escherichia coli, Bacillus subtilis and Candida albicans cultures, while methanol extract dilutions were added to HTC-15, OVCAR, UISO and KB cell line cultures. Doses of 0.4 and 0.2 mg/mL of aqueous and methanol extracts increased the bone marrow cell concentration by 2.70- and 3.15-fold, respectively, and increased the spleen cell concentration by 3.38- and 6.39-fold, respectively (p < 0.001). Aqueous extract inhibited Bacillus subtilis growth from 78 to 21%; hexane extract inhibited the growth of Escherichia coli, and methanol and chloroform extracts weakly inhibited the growth of Bacillus subtilis and Escherichia coli, respectively. Methanol extract (1 microg/mL) decreased the UISO and OVCAR cell concentrations to 59 and 82%, respectively. Data demonstrate for the first time that Plantago major has hematopoietic activity in vitro.