Results from the first high-power two-frequency heating experiment to employ obliquely incident modifying waves are presented. Diagnostic instruments measuring the effects at HF and ULF were deployed in the skip zone of the modifying waves to investigate aspects related to HF sidebands. Although occurring far less frequently than with vertically incident heating, HF sidebands were observed on a number of occasions. Two categories of sideband excitation mechanisms are currently recognized (phase modulation and downconversion) and could be responsible for the observed sidebands. Theoretical initiatives are needed to help sort out the contributions of these processes during oblique heating. ¿ American Geophysical Union 1993