The present investigation was a step toward a more thorough explication of the amount of genetic and environmental variance in vocational interests than has been found in past research. A comprehensive behavioral genetics research design was employed, using previously collected data from twins reared together, twins reared apart, adoptive families, and biological families. The data consisted of item responses from the Strong Vocational Interest Blank/Strong Interest Inventory (SVIB/SII). All of the data were scored using the Hanson Combined Form Scales for the SVIB/SII (Hanson, 1982). Correlations were computed, and model fitting analyses were run to estimate additive genetic, nonadditive genetic, shared environmental, and nonshared environmental effects. The results suggested that, on average, the variance in a wide range of vocational interests can be attributed to 12% additive genetic and 24% nonadditive genetic effects and to 9% shared environmental and 55% nonshared environmental effects and measurement error.