Patients with differentiated thyroid carcinoma (DTC), who have undergone thyroidectomy and radioablation with iodine (131I), are usually monitored with ultrasonography (US) of the neck, 131I whole body scan (WBS), and determination of thyroglobulin (Tg) concentrations in serum. A chromatographic method (CHROM), designed for detection of in vivo labeled thyroid hormones (131I-T3/T4) that circulate in the body after administration of 131I for a WBS, may be used in monitoring of these patients. This study included 35 patients with DTC. Ultrasonography, WBS, Tg, and CHROM method were performed for each of them. One patient was followed-up 6 times, 11 were monitored twice, and the remaining group of 23 patients was examined only once (51 diagnostic tests). We found CHROM results to be in disagreement with the WBS and/or Tg findings in three patients out of 35 at the time of the first visit. In one of them WBS was negative, while Tg and CHROM findings were positive. In this patient the local metastases were proven by US with fine needle biopsy (FNB). In another patient (without signs of thyroid tissue remnant, determined by WBS, Tg, and US) only CHROM was positive. Finally, in the third patient, a thyroid remnant was proven positive on WBS and US (negative CHROM and Tg). We registered an additional peak (peak 4) in chromatograms of 12 out of 35 patients. This component could be tentatively characterized as 3,3'-diiodo-L-thyronine (131I-3,3'-T2). Although this preliminary study included a small number of patients, we show that the CHROM method can be useful as an additional test in monitoring of patients with DTC, especially those with discordant WBS and Tg results.