The present 18th volume differs from previous volumes insofar as, with the exception of two contributions, it is exclusively concerned with problems of a single field, namely Tropical Medicine. This was occasioned by the International Symposium on the investigation and treatment of infectious tropical diseases held in Bombay in January 1974 and organized by the editor in collaboration with the Minister of Health of the State of Maharashtra, Dr. Rafiq Zakaria, the Director of the Hafl'kine Institute, Dr. B. Gaitonde, and with Dr. J. N. Banerjee, Dr. S. K. Bhattacharya and Mr. P. D'Souza. The Hafl'kine Institute celebrated on this occasion the 75th year of its existence and everyone entrusted with the organisation of the Symposium considered themselves fortunate to have been able to help in strengthening the contacts between Indian and foreign research workers, in the hope of, in this way, making a contribution to the fight against infectious tropical diseases. The editor hopes that the present 18th volume will represent comprehensive information on the topics treated at the Symposium; the 19th volume, which will soon appear, is concerned with the same area, so that the two volumes together should give a good picture of the many still unsolved problems. The editor would also like to take this opportunity of expressing his gratitude to his collaborator, Dr. A. Niif, who, as usual, performed valuable services in working over the manuscripts.