“…This has been used to diagnose delayed hypersensitiv ity in vitro (lymphocyte transformation test; LTT). Some metal compounds such as cobalt chloride [23], nickel salts [6,7,11,19], potassium dichromate [9], have similarly been reported to cause a specific trans formation of sensitized human lymphocytes and the possibility to diagnose contact allergy by an in vitro test has been suggested. However, there are also re ports of a nonspecific stimulating effect on unsensi tized human peripheral blood lymphocytes by mercu ric compounds [4,8,18], nickel salts [1,2,10,14,20] and zinc compounds [3,16], Similarly, peripheral adult rabbit, rat and guinea pig lymphoid cells were stimulated by mercuric chloride [15] and human cord blood lymphocytes by mercuric compounds [4], nick el sulfate [1] and zinc compounds [16],…”