Golgi impregnation was used to study the morphology, morphometry and number of mitral cells in control and stimulus-deprived olfactory bulbs (OB) of 25-day-old albino rats. The rats were made unilaterally anosmic by closure of one nostril in the early neonatal period. The previously described reductions in the size of OB and thickness of OB layers were confirmed. Quantitative comparison of the control and anosmic OB revealed that in the odor deprived OB the number of Golgi impregnated mitral cells was 40% less and the impregnation of dendritic neuropil in the external plexiform layer was greatly reduced. Of the remaining mitral cells of the odor-deprived OB, a small portion exhibited an 'atrophic' appearance with markedly reduced impregnation of the intracellular material, while the majority showed relatively 'normal' morphology. Morphometric measurements and statistical comparison of the means revealed that in the remaining 'normal' mitral cells, there were significant reductions in the following parameters: (1) the size of the cell soma as measured by the vertical and transverse diameters (17 and 12%); (2) length of the apical dendrite (27%); (3) diameter of the glomerular tuft (22%); (4) total length of the basal dendrites (18%); (5) diameter of the dendritic field of the basal dendrites (22%). The pattern of impregnation did not differ between the control OB of the experimental rats and the normal OB of normal rats. The results indicate that an absence of olfactory stimulation during the postnatal period exerts deleterious transneuronal influences on the developing mitral neurons, leading to atrophy and loss for some and diminished somatic and dendritic growth for others.