The possible effects of antipsychotic agents on haematological parameters of psyhcotic patients placed on combination therapy were studied. This is in view of some toxicological events on haematopoietic cells and haematimetric parameters usually accompany administration of some chemotherapeutic drugs. Sixty (60) individuals consisting of thirty two in-patients (male and female) receiving treatment at the Mental Health Ward, Ladoke Akintola University of Technology Teaching Hospital Osogbo and twenty eight apparently healthy individuals who served as controls were involved. Haematological parameters were estimated in all the samples using Sysmex KX-21N auto-analyzer with Erythrocyte Sedimentation Rate (ESR) estimated by Westergren method. Ion selective electrode method was used in estimating the lithium level of the samples. Results show that there is an elevated erythrocyte sedimentation rate in the psychotic patients than in the control group which is statistically significant (p<0.05). There is no significant difference (p>0.05) in the packed cell volume, haemoglobin concentration, white blood cell concentration and platelet levels between the patients and the controls. However, there is a statistically significant increase (p<0.05) in the mean cell volume, mean cell haemoglobin and mean cell haemoglobin concentration in the psychotic patients as compared with the controls. There is also no statistically significant difference (p>0.05) in the lithium level between the psychotic patients and the control. This study reveals that the antipsychotic drugs could have increased the plasma protein content in the patients as a result of inflammation or possible agranulocytosis. Hence, a careful assessment of haematological parameters before and during neuroleptic drug treatment could serve as an important means for monitoring various changes associated with the drug intake.