- During an 18 month period, a total of 4796 stool specimens collected from 151 Bedouin children enrolled in a cohort study and followed from birth, were screened for Giardia intestinalis, Cryptosporidium spp. and other intestinal parasites. Specimens were collected in phenol-alcohol-formalin (PAF) preservative and examined prior to, and after, formalin-ether concentration (FEC). During 6 months of the second year Giardia intestinalis was observed in 17.6% of the specimens and Cryptosporidium in 0.9% as compared with 1.8% (Giardia intestinalis) and 1.6% (Cryptosporidium) observed during the first year. Giardia intestinalis was detected in 8.4% (407/4796) of all the samples examined and Cryptosporidium in 1.3% (63/4796). Other intestinal protozoan parasites and helminthic ova demonstrated in the stool specimens included: Entamoeba coli (0.1%); Entamoeba histolytica (< 0.1%); Hymenolepis nana (0.1%); and Trichuris trichiura (< 0.1%). Mixed infection with 2 parasites was observed in 0.3% of the specimens. PAF fixation was found to be highly effective in preserving the integrity and antigenicity of both Cryptosporidium-oocysts and Giardia intestinalis-cysts. The detection rate of Giardia intestinalis and Cryptosporidium before FEC was not significantly different from that obtained after FEC, showing differences of only 1% and 3% for Giardia intestinalis and Cryptosporidium, respectively.