We have reviewed formaldehyde-releasers used in metalworking fluids (MWFs) in this and a previous part of a two-part article. These biocides do not appear to be frequent or important sensitizers. Even in highly selected patient groups of metalworkers, mean prevalence rates of sensitivity are low: 0.2% for Tris(hydroxymethyl)nitromethane, 1.6% for tris(N-hydroxyethyl)hexahydrotriazine, 1.9% for Bioban P-1487 and Bioban CS-1246, and 2.8% for Bioban CS-1135. In the case of the Biobans, many reactions may have been irritant. Only N,N'-methylenebis(5-methyloxazolidine) has a fairly high mean score of 4.0% in metalworkers. With the exception of Bioban P-1487, there is a clear relationship between positive patch test reactions to the releasers and formaldehyde sensitivity: 40-70% of reactions to releasers occur in patients sensitive to formaldehyde and may therefore be caused by formaldehyde allergy. There is a lack of reliable data on the clinical relevance of contact allergy to the formaldehyde releasers in MWF. In most studies, no data on relevance were provided and in those that did, relevance was often found for a (very small) minority of the reactions only. Also discussed here are the formaldehyde-releasers MDM hydantoin, methenamine, N-methylolchloracetamide, paraformaldehyde, and Preventol D2.