Zoos and the science of parasitology have developed and flourished together in a fruitful symbiosis. Interest in exotic animals has inevitably led to an interest in the creatures they bring with them, and zoos continue to provide a seem- ingly endless source of materials for biologists of every kind. The Zoological Society of London was founded in 1826 for 'the advance- ment of zoology and animal physiology'. It has always had veterinarians to care for the health of the a.nimals, to carry out post-mortem studies and to provide a wealth of bacteria, fungi, protozoa, helminths and arthropods for an avid circle of recipients. In 1919, Ronald Leiper of the London School of Tropical Medicine directed the Prosec- torium and 'arranged for the careful collection and study of all parasites, internal and external, by various ex- perts... The types of new species were presented to the British Museum (Nat. Hist.)' (Ref. I). For many years, blood films and faecal samples from new ar- rivals, animals in hospital and those that had died were collected every week for examination at the Wel come Bureau of Scientific Research in Euston Road. The Proceedings of the Zodogicdl Society of London contain frequent contributions from C.M. Wenyon and C.A. Hoare on protozoa, and from W.N.F. Woodland on helminths found in these specimens. The Zoo itself provided accommodation for students to collect and examine specimens of all kinds. At the turn of the century, before the formation of specialized learned so- cieties to cover the various aspects of biology, a meeting of the Zoological Society provided one of the few oppor- tunities available for the reporting and discussion of new observations and theories. A good example is the argu- ment about the taxonomy of schisto- somes. Theodore Bilharz and his arrogant successor at the Cairo laboratory, Arthur Loos, thought that the oc- casional egg they foun,d with a lateral spine was merely a variant of the normal, terminally spined egg of Schisto- soma haematobium. But clinicians such as Manson and Sambon were impressed by the differences the'/ observed be- tween patients: those with terminally spined eggs had haematuria and bladder pathology whereas the laterally spined eggs were associated with lesions of the gut. Manson suggested that 'possibly there are two species of Bilharzia' and Louis Sambon, at a meeting of the Zoological Society on 19 March, 1907 proposed that 'in appreciation of this, one of his many genial intuitions', the species with lateral spines should be dedicated to him and called S. mansoni 2. Loos pooh-poohed the idea and it was not until 1915, when war drove the Germans from Egypt, that Leiper was able to show that cercariae from the two types of egg infected two entirely different species of snail. The treatment of tropical disease has greatly benefited from the connexion between parasitologists and zoos. Organisms have been provided for the study of life cycles, immune reactions and susceptibility to chemicals, both in vitro and after transfer suitable lab- oratory animals. Captive canaries and monkeys yielded the parasites used in Germany for the discovery of the aminoquinoline antimalarials, and Plas- modium Iophurae, passaged in ducklings for screening compounds on a large scale in America, came from a fire- breasted pheasant in the New York