Assessing the risk of cross-infection in a liquid nitrogen storage vessel or indeed from a vapour vessel, is almost impossible, therefore common sense must prevail. We have to take every available practical step to reduce the risk of transmission. A recent article (Clarke, 1999) described a number of failings in some of the practices currently used in sperm cryopreservation and put forward some simple yet sensible suggestions to improve on them. The areas highlighted in his paper should be viewed as `good practice' and considered alongside storage in the gaseous phase. For example: straws should be manufactured from material which will not shatter after being subjected to ultra-low temperatures; filling and sealing protocols should be reviewed, in particular the use of polyvinyl alcohol powder, which is both an ineffective sealant and a potential source of contamination; vials should not be used in liquid nitrogen unless used with a second skin e.g. cryoflex or used with lids which contract and expand at the same rate. New straws are now available with filling and sealing protocols that should reduce the risk of contamination, for example the I.M.V. Cryobiosystem. To add to these recommendations, we could add that treatments performed using stored spermatozoa should involve a preparation step using density gradients and sperm washing techniques to reduce a potential viral load of the sample (Kim et al., 1999; Levy et al., 2000). Simple intra-cervical inseminations, which therefore potentially carry a higher risk of transmission, should perhaps be avoided. A similar precaution could be taken prior to freezing, aimed at reducing the viral load of the sperm tank.