Ortho-tolidine was found to greatly enhance a partial palm print in blood on a plaster wall in one homicide case and on the victim's back in another case. The print obtained in the second case made possible the identification and eventual conviction of a suspect. The forensic experts had spent over 4 hours in a small building while using the chemical. They did not use protective clothing or a breathing apparatus. They subsequently experienced severe headaches, lasting several days, as well as burning sensations on the parts of their bodies in contact with the chemicals. Ortho-tolidine was later found to be carcinogenic and its use was discontinued. In 1983 the use of tetramethylbenzidine was proposed. It was not listed as carcinogenic. Although it has been very effective in blood print enhancement and development, extreme caution should be used. An air canister should be used to spray the chemical. Blood analysis should be done before the spraying, as should photography of all visible ridge characteristics. A well-ventilated area or a vent hood should be used. The use of protective clothing, elimination of flame or spark, and avoidance of spraying live skin tissue are also recommended. Photographs and further safety instructions are supplied.