Bovine serum is an essential factor for the continuous in vitro growth of Babesia bovis parasites. Culture media typically contain 40% (v/v) of bovine serum. In the present study assays with low-serum media were performed. The growth of B. bovis Mo7 was successively lower in media with 30%, 20% and, principally, with 10% of serum. Without serum, the parasites were not able to propagate. In media with 10% of serum, the supplementation with Albumax (TM) II improved visibly the growth of B. bovis at the end of each cycle. Regarding the addition of orotic acid, no considerable effect was observed in media with 20% or 10% of serum, with or without Albumax (TM) II. B. bovis parasites cultured in vitro in all these media maintain their typical morphology during the intraerythrocytic stages.