Men affected by CatSper- or Slo3-related infertility will be identified through the CatSper-Test, interrogating the biobanks and databases of the CeRA and the Center for Medical Genetics, and genome sequencing. Since currently available inhibitors do not distinguish between the two channels, it remains unclear how selective channel inhibition affects sperm function. Therefore, sperm from infertile men mith loss of CatSper or Slo3 will be comprehensively phenotyped and compared with sperm from fertile donors, and the action of novel CatSper and Slo3 inhibitors will be analyzed.