The sensitizing capacity of 4,4(1)-dihydroxy-3-(hydroxymethyl)-diphenyl methane (4,4(1)-H-3-HPM), 4,4(1)-dihydroxy-3,3(1)-di-(hydroxymethyl)-diphenyl methane 4,4(1)-H-3,3(1)--HPM) and 4,4(1)-dihydroxy-3,5-di-(hydroxymethyl)-diphenyl methane (4,4(1)-H-3,5-HPM) was investigated using the guinea pig maximization text. These compounds are known contact sensitizers in phenol-formaldehyde resins (P-F-R). The study was performed in order to assess and compare the degrees of the sensitizing capacities of these chemically related substances. The animals were also rechallenged with the sensitizer and 5 related compounds, all known to be present in P-F-R, in order to study the cross-reaction patterns. 4,4(1)-H-3,3(1)-HPM was demonstrated to be a strong sensitizer and 4,4(1)-H-3-HPM and 4,4(1)-H-3,5-HPM to be moderate sensitizers. With 4,4(1)-H-3,3(1)-HPM as the sensitizer, 4,4(1)-H-3-HPM and 4,4(1)-H-3,5-HPM were cross-reacting substances and simple methylol phenols were possible cross-reacting compounds. Possible cross-reactivity were indicated between the three 4,4(1)-H-HPM when 4,4(1)-H-3-HPM and 4,4(1)-H-3,5-HPM respectively were the sensitizers. The chemical investigation by high pressure liquid chromatography indicated that the compounds tested were pure and separable.