The present research investigated the importance in schizophrenia of concrete thinking, personally overinvolved thinking, and idiosyncratic or bizarre thinking. Seven indices of thinking were derived from three tests administered individually to 45 acute schizophrenics and 47 nonschizophrenic psychiatric patients. Although the concrete thinking of the schizophrenic has been emphasized by some, the present data do not support this factor as a pervasive feature in relatively early acute schizophrenia. Schizophrenics tended to be more concrete than nonschizophrenics. Concreticity, however, was not a frequent characteristic among any of the major diagnostic groups. Schizophrenic patients had significantly more idiosyncratic thinking than nonschizophrenic patients (P< 0.001). Personally overinvolved thinking was slightly more frequent in acute schizophrenics, but was also found in many acutely disturbed nonschizophrenics. The results suggest that strange, idiosyncratic thinking is a more important characteristic of acute schizophrenia.