Africa, the "dark continent" and the source of such wonderful tales as King Solomon's Mines and Jock of the Bushveld, has an equally enthralling story to tell about malignant disease in general and the lymphomas in particular as they occur among its varied people. It is uncertain how far back in history contact existed with the rest of the world, primarily in the form of slave trading and colonization by, among others, the Portuguese and the British. Until recent times, however, Africa's secrets have remained largely undisturbed. Fragments of medical information are recorded in the diaries of those early, intrepid explorers, such as Albert Cook, Henry Stanley, David Livingstone, and Albert Schweitzer. However, it is only in recent years that the great natural experiments that have for so long been underestimated, and very much less understood, belatedly started to attract attention. Examples are the systematic studies by Denis Burkitt, who through perseverance unraveled the lymphoma that now bears his name, and the thought-provoking description of the immunoproliferative small intestinal disease carried out by the Cape Town group, with both illustrating the axiom that "the study of man is man." Despite such occasional outstanding achievements, there is still considerable paucity of data pertaining to the various lymphoreticular malignancies, so that only limited conclusions are possible. Certainly, lymphoma in Africa differs from that elsewhere in the world. In part, this may reflect a background of immunologic disturbance attributable to parasitic infestation, viral infection, rampant malnutrition, and the impact of a wide variety of vectors, such as mosquitoes, in disease transmission. Striking differences exist in the distribution of these tumors as the incidence and pattern are followed from the equator to the milder climates in the south. This confirmed phenomenon gives rise to the tantalizing suggestion that, to some significant extent, the changes reflect the influence of geography. Thus, there may be associated alterations in the fauna and flora that determine the presence of intermediary hosts that have an impact on the eventual expression of the malignant clone. Many questions remain unanswered. For example, how can the lower incidence of Hodgkin's disease and the predominance of high-grade malignancies in the tropics and subtropics be explained? To what extent does the lymphocytic and plasmacytic hyperplasia, ascribed to intense antigenic stimulus in Burkitt's lymphoma and myeloma--perhaps even other lymphomas, such as IPSID--predispose the host to a mutational event that leads to the emergence of each distinctive neoplasm?(ABSTRACT TRUNCATED AT 400 WORDS)