Yes, BrdU (Bromodeoxyuridine) can be in vitro as well as in vivo in cell proliferation studies. There are several different protocols for BrdU labeling in vitro. In general, primary cell cultures or cell lines can be incubated with BrdU at a final concentration of 10 µM (diluted in cell culture medium). As with all procedures, it is important that the protocol be optimized for your specific assay system before proceeding.