The normal 'reference' ranges of haematological parameters vary considerably under the influence of different factors, such as the age and sex, and various environmental factors. Furthermore, diurnal variations have also been observed. In this study the normal 'reference' ranges of haematological parameters established by analysing samples from 804 healthy Saudi students (578 males and 226 females), with ages ranging between 20 and 29 years, are presented. Comparison of the results from males and females shows that all values are higher for the Saudi males than for the females except values for white blood cell counts. Comparison of the mean values for Saudi with the values for the western population shows that for the Saudi male the mean values for Hb F is slightly higher while for all other parameters the values are lower. Among the Saudi females mean values for Hb F, white blood cell counts and mean cell volume are slightly higher than those reported for western females. Mean values for all other parameters are lower than corresponding mean values in westerners.