Flea assemblages of Meriones crassus Sundevall and Gerbillus dasyurus Wagner in different habitats in the Negev Highlands of Israel were studied to determine how flea abundance and species composition on the same host change among habitats, and the environmental parameters determining specific composition of flea assemblage. Fleas of the same species parasitizing different hosts responded differently to the same set of environmental variables. Spatial distribution of fleas on M. crassus was determined by environmental parameters significantly stronger than those on G. dasyurus. Flea abundance and species composition on both host species changed among habitats. Indirect ordination of flea assemblages produced axes that presented spatial components of change in flea composition (for M. crassus--Xenopsylla conformis Rothschild versus Xenopsylla ramesis Rothschild; for G. dasyurus--Xenopsylla dipodilli Smit versus X. conformis and X. ramesis versus X. conformis). Discriminant analyses of flea assemblage on M. crassus demonstrated that fleas were segregated along 2 discriminant axes that reflected a soil structure and productivity gradient and a contrast between dry riverbeds and watershed plains. Ordination of flea assemblages on G. dasyurus produced 2 discriminant axes, both presenting a complex gradient of the soil structure and the level of primary production.