Hodgkin's disease (HD) and Ki-1 positive anaplastic large cell lymphoma (Ki-1 ALCL) appear pathologically and immunohistochemically related, and a common histogenesis has been postulated in at least some cases. The breakpoints of the t(2;5) (p23;q35) [corrected] translocation, which is reported in about 40% of Ki-1 ALCL, have recently been cloned. They involve a novel tyrosine kinase gene, ALK, at 2p23 and the nucleophosmin gene, NPM, at 5q35. Reverse transcriptase polymerase chain reaction (RT-PCR) using NPM and ALK primers consistently detects a fusion product in Ki-1 ALCL cases with the translocation. To determine if this tumor-specific genetic alteration also occurs in HD, we performed NPM-ALK RT-PCR on RNA samples extracted from 40 lymph node biopsies of HD (25 nodular sclerosis, 11 mixed cellularity, 2 lymphocyte depleted, 2 lymphocyte predominant). Using control samples, the sensitivity of the NPM-ALK RT-PCR assay was shown to be at least 1:10(4). Amplifiable template was confirmed in all samples by RT-PCR using beta-actin primers. None of the 40 cases showed the expected 177-bp RT-PCR product indicative of the translocation. We conclude that the most common primary genetic alteration in Ki-1 ALCL, the t(2;5), is absent or very infrequent in typical cases of HD. These results further support the concept that HD and Ki-1 ALCL are pathogenetically distinct entities.