The analysis of the production of fortis and lenis plosives in German has shown the importance of the duration ratio vowel/ (vowel + closure) for the distinction. To complement these results a perception test was carried out in which 29 native speakers identified a randomised sequence of 220 stimuli from tape as one of the phrases ‘Diese Gruppe kann ich nicht leid(e)n (leit(e)n)’. The stimuli were obtained from the two naturally produced originals by changing the ratios and the length of voicing in the plosive through computer processing. The test results indicate very conclusively that judgment can be reversed simply by changing the ratio to the appropriate ones found in production. There is a hierarchy of perceptual dimensions: duration ratio > formant transition > voicing.