The possibility of transmission of virus particles from patient to patient by multi-use silver nitrate sticks and styptic pencils and by cotton wool swabs that have been dipped repeatedly into Dewar flasks of liquid nitrogen was studied. The results showed that transmission by the sticks and pencils is unlikely but that virus particles can be transferred into and out of a Dewar flask on cotton wool swabs. We suggest that swabs should not be dipped repeatedly into the flask of liquid nitrogen but that, instead, a small aliquot of nitrogen should be decanted into a smaller 'clean' vessel and a new cotton swab used for each patient.