This paper reports results of a study on self-monitoring in speech production. Thirty schizophrenics, varying in verbal hallucination and in negative symptoms status, and 17 controls were tested on the reporter test. The position of interruptions of the speech-flow to repair errors was used to indicate whether the detection of the errors was through monitoring of internal phonetic plans or through external acoustic feedback. We have found that the internal error detection was twice as frequent in controls as in schizophrenics. The relevance of this finding to Frith's (1992) model of schizophrenia is discussed. Our conclusion is that the problem with internal monitoring of phonetic plans is common to all schizophrenics, and not just to those with verbal hallucinations.