An investigation was undertaken to study the mode of inheritance of apholate resistance in Aedes aegypti (l) . Sterility-concentration curves were determined for each sex of the resistant, susceptible, and F1 hybrid genotypes. The SC50 values were 48.30 for the resistant male, 2.26 for the susceptible male, 4.14 for the F1 male (resistant female x susceptible male), and 19.50 for the F1 male (susceptible female x resistant male); and 31.6l for the resistant female, 3.22 for the susceptible female, 8.94 for the F1 female (resistant female x susceptible male), and 16.87 for the F1 female (susceptible female x resistant male) . The results of genetic crosses indicated that apholate-resistance in A. aegypti was a quantitative trait with a marked paternal influence on the resistance of F2 and back-cross progeny. There was no marked cross -resistance to tepa and metepa in the apholate-resistant strain, but increased tolerances to both chemicals were found. There was no loss of resistance through 9 generations after selection pressure was removed from a sub-colony of the apholate-resistant strain. The examinations of chromosome squashes were negative for major chromosomal aberrations in the apholate-resistant strain.