THE HYPOTHESIS IS THAT CRIMINALITY IS BIOLOGICALLY INHERITED, THEN THE BIOLOGICAL PARENTS OF CRIMINAL ADOPTEES SHOULD CONTAIN A SIGNIFICANTLY GREATER NUMBER OF CRIMINALS THAN THE ADOPTIVE PARENTS. SEVENTY OF THE BIOLOGICAL FATHERS OF THE CRIMINAL ADOPTEES WERE FOUND TO BE CRIMINALS COMPARED TO 40 OF THE BIOLOGICAL FATHERS OF THE CONTROLS. WITHIN THE LIMITATIONS OF THE METHODOLOGY THIS WAS TAKEN TO INDICATE A HEREDITARY FACTOR IN THE ETIOLOGY OF CRIME. THIRTY-THREE OF THE ADOPTIVE FATHERS OF THE CRIMINAL CASES WERE REGISTERED AS CRIMINALS AS AGAINST 14 OF THE CONTROL ADOPTIVE FATHERS. PROPORTIONATELY SIMILAR DATA WAS OBTAINED FOR THE MOTHERS. A CROSS-FOSTER COMPARISON INDICATED THAT THE HEREDITARY EFFECT WAS IN THE DIRECTION OF BEING MORE IMPORTANT THAN THE ENVIRONMENTAL EFFECT INDEXED IN THIS WAY. THE PSYCHIATRIC RECORDS OF THE CRIMINAL AND NON-CRIMINAL SUBJECTS WAS COMPARED ACCORDING TO THE SAME DESIGN. ALSO DISCUSSED ARE THE HISTORIES OF MENTAL ILLNESS IN THE RESPECTIVE PARENTS. (AUTHOR ABSTRACT)