Based on the interaction of eye and hand movements a comprehensive index summarizing schizophrenia patients' difficulties during the performance process in Trail-Making Test-B (TMT-B) was developed. The process of TMT-B performance was modelled as a sequence of planning, acting and resting periods in 23 inpatients with acute schizophrenia, 17 inpatients with acute depression and 21 non-psychiatric controls, each assessed at least twice within four weeks. Transition probabilities between these states were calculated and structured by factor analysis. Throughout their hospital stay schizophrenia patients scored significantly lower than non-patients on a derived "visuo-manumotor integration factor", characterized by high loadings of transitions between planning and acting periods. A significant negative correlation of this factor with performance time revealed frequent alternations between these two states and thus high factor scores to be a prerequisite for good TMT-B performance. No relationship of factor scores with psychopathology and medication could be found. Depressive patients differed neither from non-patients nor from schizophrenia patients during the acute phase of the illness, but scored significantly higher than schizophrenia patients shortly before discharge. Accordingly, poorer TMT-B performance in schizophrenia patients seems related to impaired planning strategies, which might be a nosologically specific, trait-like characteristic, probably related to neural dysfunctions involving the prefrontal cortex.