New techniques in Czech derivational morphology are discussed. They are based on the exploitation of the tool Deriv with integrated access to the main Czech dictionaries and corpora (SYN2000c and the new large Czech corpus CzTenTen12). The case study deals especially with the Czech suffix -ák -we describe its behaviour as completely as possible. The paper brings some new results in comparison with standard Czech grammars which do not rely on large data and software tools.