TABLE 3. Relative Potency Factors (RPFs)^a and Rank Order of Potency.

	Most potent					Least potent
AFC/106 spleen cells:
Chemical	TCDD	TBDF	4PeBDF	1PeBDF	TCDF	4PeCDF	1PeCDF
ED50	0.34	3.87	8.17	42.79	55.3	59.96	696.4
RPF	1.0	0.09	0.04	0.008	0.006	0.006	0.0005
AFC/Spleen:
Chemical	TCDD	TBDF	4PeBDF	TCDF	4PeCDF	1PeBDF	1PeCDF
ED50	0.32	3.61	6.07	34.12	35.92	45.63	573.5
RPF	1.0	0.088	0.052	0.009	0.009	0.007	0.0006
Serum IgM antibody titer to SRBCs:
Chemical	TCDD	4PeBDF	TBDF	4PeCDF	TCDF	1PeBDF	1PeCDF
ED50	1.87	16.89	19.31	126.3	180.2	181.1	529.0
RPF	1.0	0.110	0.097	0.015	0.010	0.010	0.004
Cyp1a1 expression:
Chemical	TCDD	TBDF	4PeBDF	1PeBDF	TCDF	4PeCDF	1PeCDF
ED50	1.22	13.39	21.84	83.74	128.6	129.2	169.1
RPF	1.0	0.091	0.056	0.015	0.010	0.009	0.007
Cyp1a2 expression:
Chemical	TCDD	TBDF	4PeBDF	TCDF	1PeBDF	4PeCDF	1PeCDF
ED50	2.43	23.17	33.06	138.7	161.5	184.5	189.8
RPF	1.0	0.11	0.074	0.018	0.015	0.013	0.013

Note. TriBDD was not included in the RPF assessment due to a lack of a statistically significant effect. DBDCDD was not included in the RPF assessment due to a nonmonotonic dose response.

^aRelative potency factors were calculated as the ED50 (g/kg) value (from the Hill model) for TCDD/ED50 (g/kg) value for the test chemical.