The current paper proposes a biomedical image watermarking technique through modified bit replacement algorithm in spatial domain. In this algorithm, multiple copies of the same information are hidden in the biomedical images. Detection is performed by applying bit majority algorithm which can reconstruct the hidden information from different recovered sets subjected to some common attacks. Keys for watermark recovery are also embedded in the cover image. The superiority of the proposed modified bit replacement scheme over the LSB technique is indicated through evaluation of image quality metrics that shows much enhancement in the visual and statistical invisibility of hidden data.