Manoel Antonio da Fonseca Costa Filho, M.Sc., Consultant in Quality Assurance, Biomanguinhos/ FIOCRUZ, Brazil Dr Jorge F. Gomez Herrera, Director of Quality Assurance, Gerencia General de Biologicos y Reactivos, Secretaria De Salud, Mexico WHO/VSQ/97.02 ENGLISH ONLY DISTR.: LIMITED World Health Organization Geneva 1997