Wildlife extinctions are thought to be occurring more rapidly than at any time in the history of the earth, mainly because of human activities. These include agriculture, urbanization, deforestation and a myriad other processes. While it is impractical to think that reproductive technologies could be used on a grand scale to help save large numbers of species from extinction, the judiciously targeted use of some simple technologies should be useful in helping to support the viability of small populations facing genetic problems such as inbreeding. In fact, it has long been proposed that banks of frozen spermatozoa could be used as adjuncts to captive breeding programmes, thus allowing genetically valuable males to continue contributing to the gene pool long after their death. Unfortunately, this scenario has yet to be realized at a practical level. Much of the problem lies with the difficulty of establishing successful cryopreservation techniques for different species; working with diverse taxonomic groups regularly requires us to revise our approach to cryopreservation technology. Marsupials are an interesting case in point as many species are threatened and there is considerable interest in establishing genetic resource banks for species under threat, including the Tasmanian devil, koala and various wallabies and kangaroos. There is the unexplained observation that marsupial spermatozoa require more than double the cryoprotectant concentrations typically used with eutherian species; for example, more than 15% glycerol is required for wallaby and kangaroo sperm cryopreservation in order for any motility to be retained after freezing and thawing. This may reflect a distinctly different organization in plasma membrane structure between (some) marsupials and eutherians. In addition, marsupials also package DNA in their sperm heads rather differently from eutherians; their version of protamine 1 and 2 does not contain the disulphide-bond forming cysteine groups that produce the rigid chromatin structure seen in eutherians. This means that marsupial sperm heads are sometimes, but paradoxically not always, easily disrupted by freezing and thawing. In addition to the species differences themselves, relatively recent research findings about mammalian sperm function indicate that they undergo extensive and complex interactions with the female reproductive tract before they reach the site of fertilization. Sperm cryopreservation is now known to change these interactions, resulting in poorer ability to establish the sperm reservoir within the oviductal isthmus. In addition, we also know that semen samples contain functionally and morphologically distinct subpopulations, where some subpopulations seem more sensitive to cryoinjury than others. It seems that the realistic development of working genetic resource banks for wildlife conservation still, unfortunately, requires dedicated and species-focused research approaches. If all species had the same sperm, life would be so much easier! Source of funding: None declared. Conflict of interest: None declared. Bill.holt@sheffield.ac.uk