The protein truncation test (PTT) is a simple and fast method to screen for biologically relevant gene mutations. The method is based on the size analysis of products resulting from in vitro transcription and translation. Proteins of lower mass than the expected full-length protein represent translation products derived from truncating frame shift or stop mutations in the analyzed gene. Because of the low sensitivity of the conventional PTT mutations can be detected only in those samples, which harbor a high relative number of mutated gene copies. This disadvantage can be overcome by technical modifications and advanced forms of the PTT. Modifications like gene capturing and the digital PTT lower the detection limit and thus allow the use of the PTT in the detection of mutations in body fluids. Another disadvantage of the conventional PTT is the use of radioactive labels for protein detection. Recently, modifications like fluorescent labels or the use of tagged epitopes were established, which allow the detection of the nonradioactive translation product. When several epitopes in different reading frames are used, the mutation detection spectrum can be expanded to all possible frame shift mutations. These modifications transform the PTT into a powerful nonradioactive technique to detect mutations with high sensitivity.