Samples of milk from 23 mothers attending the department of obstetrics and gynaecology and 36 who donated milk to the department's milk bank were cultured for cytomegalovirus. Virus was isolated from samples from 12 of the milk donors but none of the mothers attending the department; follow-up studies during lactation in seven of these 12 women showed that five continued to excrete the virus. Samples were taken on three occasions from one woman who regularly excreted high titres of the virus. Storage at -20 degrees C for over three days reduced the titre by over 99%; after pasteurisation at 63 degrees C for eight minutes the milk did not contain any viable virus. It is recommended that raw banked milk used for feeding preterm babies should be kept frozen for at least 72 hours before feeding.