Nucleolar organizer regions (NORs) are important for regulating protein synthesis. Our study points towards the possibility of determining gut-associated lymphoid (GAL) cell proliferation and maturation in fetuses from ten to 35 weeks of gestation by means of the Argyrophilic (Ag) staining for NORs. This technique was performed on paraffin-embedded small intestine and mesentery tissue sections from 30 fetuses at the I 0th, 14th, 15th, 19th, 20th, 23rd, 31st, and 35th week of gestation. Our results showed that there was no statistically significant difference concerning the mean AgNOR values, between GAL cells and mesentery lymphoid cells (2.81 ± 0.63 to 2.63 ± 0.71; p > 0.1), from ten to 15 weeks’ gestation. In this specific period, the lymphoid cells first appear and Peyer’s patches are formed in the small intestinal mucosa. In contrast, in fetuses from 19 to 35 fetal weeks NOR counts were statistically significantly greater in GAL cells than in fetuses from ten to 15 gestational weeks (as com­pared to NOR counts in GAL cells in fetuses at an earlier fetal age) (3.28 ± 0.73 to 2.81 ± 0.63). Mean AgNOR values in mesentery lymphoid cells remained unchanged (2.62 ± 0.57) (p < 0.001). In conclusion, increasing protein synthesis from the 19th till the 35th week of gestation is indicative of immune system matura­tion, given that at the same time GAL cells become fully mature. Mesentery lymphoid cells pass (migrate) to the small intestinal mucosa from the bloodstream, and they form the whole out-associted lymphoid tissue (GALT) organ (Peyer’s patches). The lymphatics associated with mucosa associated lymphoid tissue (MALT) are all efferent; it seems that during fetal life due to genetically determined factors, draining vessels operating as afferent lympha­tics at that time, change to efferent (where the immunological response is greatly amplified) as embryonal life progresses.