Extract of Parquetina nigrescens is used traditionally to treat anaemia by Yoruba people of South Western Nigeria. There is no previous study on the stimulatory effects of the herb on lymphoid cells (i.e. CD4+ T-cells). This study determined the levels of products of bone marrow stimulation including CD4+ T-cell in Wistar rats after oral administration of aqueous extract of the leaf of P. nigrescens. Fifteen Wistar rats, divided into five groups were used for this study. Group A=untreated (controls), group B=treated with 0.008 g of extract/kg body weight (BW), group C= treated with 0.08 g of extract/ kg BW, group D= treated with 0.8g of extract/kg BW, group E= treated with 8.0g of extract/kg BW. Blood sample was collected from each rat through cardiac puncture for the determination of hematological indices (WBC, RBC, PCV, Hb, MCV, total lymphocyte and CD4+T-cells) using haemocytometer and flow cytometer respectively. Aqueous extracts of the leaf of P. nigrescens did not evoke any observable toxic effect. There were significantly (p