A postal questionnaire was sent to 11 UK Children's Cancer Study Group bone marrow transplant centres asking them for details of their instructions to patients on discharge after either allogeneic or auto transplant; nine centres responded. There was no recommendation on which they all agreed. Though all centres gave prophylactic septrin, the times of starting and stopping treatment varied considerably. Three centres recommended lifelong penicillin after total body irradiation, one treated for two years and five gave no such prophylaxis. Four of nine centres gave routine acyclovir for herpes simplex prophylaxis. Most centres suggested prophylaxis against varicella after contact exposure for one year. However, three gave zoster immune globulin alone, one gave this together with acyclovir, and five gave acyclovir alone. No two centres recommended the same dose of acyclovir. Vaccinations were allowed from 6-18 months after transplant. One centre required documentation of recovery of immune function first. Four centres recommended a child stay off school for six months; others had 'common sense' approaches. Only one centre did not allow family holidays for the first six months but many imposed restrictions on these holidays. Dietary restrictions varied greatly between centres. It is concluded that there is a need for unified and scientifically justified guidelines after transplant for paediatric bone marrow transplant patients.