A highlighting system for use with electronic circuit design tools is provided for displaying signal waveforms and Register Transfer Logic (RTL) source code portions corresponding to a selected signal in the same window. The user selects a time and signal to be explored. Based on the selected time and signal, the values of all related signals are identified from a database generated by simulation of RTL source code. Nodes corresponding to the related signals are identified from a gate-level netlist corresponding to the RTL source code and the nodes responsible for the particular value of the selected signal at selected time are identified. The nodes are then mapped on to the RTL source code portions by a process of Instrumentation. The RTL source code portions so identified are then displayed. In particular, the portions of the RTL source code responsible for the particular value or transition in particular value of the signal at the selected time are highlighted.