The localization of i.p. injected, radioiodine conjugated monoclonal antibody HMFG2 was studied in 18 patients with ovarian carcinoma. Patients were injected i.p. at time points up to 168 h before laparotomy, at which time tumor, ascites, normal tissue, and blood samples were removed and the contained radioactivity measured. In the first 10 patients, localization was compared with that of a simultaneously injected irrelevant (nonspecific) antibody (UJ13A) of the same immunoglobulin class and, in the subsequent 8 patients, with HMFG2 administered i.v. After i.p. injection, HMFG2-radioiodine was found in concentrations of 0.0001-0.0030% of the injected amount per gram in solid tumor, 0.0363-0.02560%/g in ascites, 0.0003-0.0017%/g in blood, and 0.001-0.0012%/g in normal tissue. Tumor:normal tissue ratios of 0.9-10.0 and tumor:blood ratios of 0.3-4.0 were seen up to 168 h after injection. Localization of the HMFG2 conjugate was consistently greater than that of the irrelevant antibody. For solid tumor, the i.v. route of administration resulted in consistently higher absolute levels of HMFG2 conjugate uptake but tumor:blood and tumor:normal tissue ratios were similar. On the other hand the i.p. route of administration offered consistent advantages of 4- to 71-fold over the i.v. route when HMFG2 conjugate localization on ascites cells was examined. Ascites:normal tissue and ascites:blood ratios of up to 512 and 448, respectively, were achieved. After i.p. injection, radioiodine was cleared from the body exponentially with a half-life of 50 h. Maximum circulating blood levels of 8.6 +/- 2.0% injected activity were seen at 48 h and these then decreased with a t 1/2 value of 38 h. Over 80% of injected activity was cleared in the urine as nonprotein bound iodine by 168 h.