Considerable growth of both the body and the brain occurs throughout the lifespan in goldfish. In the present study growth-related changes in the goldfish olfactory system were examined using quantitative morphometric techniques as well as [3H]thymidine autoradiography. While the two olfactory structures examined, the bulb and the rosette, grow in proportion to the rest of the animal, each structure shows evidence of differential maturation. Examination of olfactory bulb laminar volumes suggest that bulbs expand primarily by generating neuropil rather than by adding new cells. This interpretation was supported by the findings that olfactory bulb granule cells decrease in density and increase in soma size as animals grow. Additionally, virtually no [3H]thymidine-labeled cells were found in the granule cell zone. Olfactory rosettes grow by adding new lamellae to the structure's medial aspect as well as by increasing the length of existing lamellae. These findings were supported by examining [3H]thymidine-labeled cells, which were differentially distributed across the rosette, with significantly more labeled cells found medially vs laterally. Results are discussed in terms of their implications for the system's functioning during growth.