In this study, expressions of cell-cycle-related genes: p53, retinoblastoma (Rb), p21, bcl-2(alpha), bcl-2(beta); protooncogene c-ski; glial cell marker protein gene S100beta; neurotransmitter gene, substance P and sexual-differentiation-related genes, androgen receptor (AR) and estrogen receptor beta (ER(beta)), are studied in the olfactory bulb of groups of both six female and six male rats at the ages of 3, 10, 20 and 40 days. Expressions of housekeeping genes such as beta-actin, cyclophilin and proliferating cell nuclear antigens (PCNA) are determined using reverse transcription polymerase chain reaction (RT-PCR) for the correction of unequal amount of cDNA added into the samples. Using labeled 32P-dCTP and Phosphorimager technology, relative abundance of radioactivities of the PCR products is obtained by dividing the radioactivity of each individual sample by the corresponding radioactivities of different housekeeping genes. Data evaluated by Two-way ANOVA indicate that only the bcl-2(alpha) gene expression is affected significantly by age, sex and their interactions no matter which of the three housekeeping genes is used for correction. When beta-actin was used for corrections, effects of age but not sex were found in the expressions of p53, Rb, p21, AR, ER(beta), substance P and S100beta genes, but not in bcl-2(beta), c-ski, cyclophilin and PCNA genes. While cyclophilin was used for corrections, only the p53, Rb, AR, ER(beta), substance P and S100beta but not the bcl-2(beta), p21, c-ski, PCNA and beta-actin genes are affected by age. They are all not influenced by sex of the animals. Only the AR, ER(beta) and S100beta genes are age-dependent when PCNA was used for the correction. The other gene expressions are not altered by sex, while the interactions of age and sex were found to be significantly affecting the bcl-2(beta) gene expression. Conclusively, developmental changes of the p53, Rb, AR, ER(beta), substance P and S100beta genes expressions are quite evidenced while only the bcl-2(alpha) gene seems to change significantly during the sexual differentiation of olfactory bulb in rats.