The particle size distribution of bovine milk has been the subject of recent reports, and different techniques have been used to determine the range of micellar sizes. These techniques have included light scattering and centrifugal fractionation (Lin et al. 1971); electron microscopy (Schmidt et al. 1973) and chromatography and photon correlation spectroscopy (Griffin & Anderson, 1983). The size of the micelles ranges between 20 and 600 nm with a maximum frequency of around 60-80 nm as reported by Holt et al. (1978) and Kimber et al. (1978); submicellar particles were observed by Schmidt et al. (1973).Despite its economic potential, the camel and its milk have received little attention. Moreover, the camel is well adapted to arid environments and can produce milk when its water intake is drastically restricted (Yagil & Etzion, 1980). Elamin (1980) gave an account of the dromedary camel of the Sudan and its milk constituents: the percentages of water, protein and fat were 86-90, 3 -6-4"7, 4-5 -5 respectively. Ahmed et al. (1979) studied some minor constituents of camels' milk: the amounts of Ca and P (mg/100 ml) detected were 137-312 and 39-152 respectively.The casein micelle size of camels' milk is an important parameter of the structure of the milk. This was studied using transmission electron microscopy to observe the relative particle size distribution. Some observations on the structure of casein micelles, together with a comparison of their average diameter, are also given. MATERIALS AND METHODS Collection of samplesSix samples of milk were collected from six individual Bedouin camels (Camelus dromedarius), reared by nomads, from the Sudan. The samples were collected from two different semi-desert sites: (a) 50 miles N. of Wad Medani (capital of the Gezira Region), samples no. 1, 2 and 3 and (b) 10 miles S.W. of Wad Medani, samples no. 4, 5 and 6. This choice of sites enabled all the samples to be taken from camels within the first 1-2 months of onset of lactation.To let down the milk, the baby camel (calf) was introduced to suckle its mother for about 10-15 min. Then after discarding the first 2-3 strips, about 2-3 ml milk were collected directly from each camel into test tubes containing an equal volume of 25 % glutaraldehyde in 0-2 M-sodium cacodylate-HCl buffer (pH 7-2), and then fixed for 1 h. Samples were mixed with an equal volume of 2-5% molten agar (60-70 °C), and the material poured on to glass slides and allowed to set. The gel was then cut into 1 mm 3 pieces and kept refrigerated (below 5 °C) inO -2 M-sodium cacodylate -HC1 buffer (pH 7-2) ready for further processing, within 3 weeks, at Reading University, UK. Both immediate processing and alternative preparative techniques on fresh milk were impossible in these geographical sites.