VIRUSES or virus-like particles (VLPs) have been found in Entamoeba histolytica1, in the amoeboflagellate Naegleria gruberi2 and in malaria parasites3–5, but there have been no reports as yet of such organisms being found in the Trypanosomatidae. During investigations on the ultrastructure of various members of the genus Leishmania, however, VLPs have been found in the promastigote forms of an isolate of Leishmania hertigi. Leishmania hertigi6 was obtained from Panama and kept in our laboratory on blood agar slopes or as cryopreserved material at the temperature of liquid nitrogen. Examination of the promastigotes of L. hertigi immediately revealed cytoplasmic inclusions of a type which had not been observed in any of our previous studies on the promastigotes of Leishmania species in culture.