A series of experiments were performed, using a representative bunyavirus (San Angelo) and flavivirus (Kunjin), to determine some of the factors which affect transovarial transmission (TOT) of arboviruses in mosquitoes. Both inter- and intraspecific differences were observed in the TOT rates among selected mosquito populations. In addition, minor variations were also observed in the TOT rates among five strains of Kunjin virus. Serial transovarial passage of San Angelo and Kunjin viruses in mosquitoes did not change their TOT rates. San Angelo virus TOT rates in orally and parenterally infected Aedes albopictus were similar. San Angelo virus survived for 3 months in dried A. albopictus eggs maintained at 28°C, with no decrease in the percentage of infected eggs. Variation of the larval rearing temperature from 20–32°C had no effect on the TOT rate of San Angelo or Kunjin viruses in A. albopictus. Mosquitoes transovarially infected with San Angelo virus developed at the same rate and produced comparable numbers of offspring as noninfected controls. In contrast, A. albopictus larvae transovarially infected with Kunjin virus were retarded in their development. Results of this study, as well as data from other reports, suggest that the effect and possibly the mechanism of bunyavirus and flavivirus transovarial infection in mosquitoes may be different.