Nocturnally active Acomys cahirinus and diurnally active A. russatus cooccur in hot rocky deserts, and their temporal partitioning results from competition. We studied their population biology at Ein Gedi near the Dead Sea to determine their spatial relationships and gain insight into their ecological overlap. Individuals of both species were trapped repeatedly for almost 2 years. Mean body mass did not change seasonally, and A. russatus was significantly heavier than A. cahirinus. Density of A. russatus was significantly greater than that of A. cahirinus. Acomys russatus had a shorter reproductive peak that overlapped the longer reproductive season of A. cahirinus. Acomys russatus showed a significant preference for boulder habitat versus open habitat at all seasons, whereas A. cahirinus showed a preference for boulder habitat only half of the time. Sexes of both species overlapped in home range.