Radio frequency interference (RFI) can have adverse effects on commercial electronics. Current properties of high performance integrated circuits (ICs), such as very small feature sizes, high clock frequencies, and reduced voltage levels, increase the susceptibility of these circuits to RFI, causing them to be more prone to smaller interference levels. Also, recent developments of mobile devices and wireless networks create a hostile electromagnetic environment for ICs. Therefore, it is important to measure the susceptibility of ICs to RFI. In this study, we investigate the susceptibility levels to RFI of the clock network of a basic digital building block. Our experimental setup is designed to couple a pulse modulated RF signal using the pin direct injection method. The device under test is an 8-bit ripple counter, designed and fabricated using AMI 0.5 μm process technology. Our experiments showed that relatively low levels of RFI (e.g., 16.8 dBm with carrier frequency of 1 GHz) could adversely affect the normal functioning of the device under test.