The present invention relates to methods for improving the ability of spermatozoa to fertilize an egg in vitro and/or vivo, said method comprising providing a medium comprising active vitamin D (calcitriol) or analogs thereof, providing a sample of spermatozoa, and incubating said sample of spermatozoa with said medium. In addition, the invention relates to compositions comprising active vitamin D or analogs thereof for use in the treatment of infertility in a male or female subject.
