We have studied human immunodeficiency virus type 1 (HIV-1) infection in three different human neuroblastoma cell lines; SK-N-MC, IMR-32 and SH-SY5Y. In all of these cell lines the infection became productive. However, the virus expression was different as determined by the p24 antigen capture assays from culture supernatants and immunochemical (APAAP) staining of cells. The medium of SK-N-MC cells contained approximately 300 pg p24 antigen per 10(6) cells, 0.1-1% of the cells were p24 antigen-positive and characteristic genomic and subgenomic HIV mRNA species were seen in Northern blotting. In infected IMR-32 and SH-SY5Y cell cultures, the HIV-1 production was below the level of detection. However, infectious virus was found by inoculating cultures of the lymphoid cell C8166 with the cell-free supernatant fluid from the neuroblastoma cultures. The lymphoid cells became positive within one week. Moreover, phytohemagglutinin-stimulated normal human lymphocytes produced virus, if cocultured with any of the three infected neuroblastoma cell lines. The infection was persistent and has been followed, using the above techniques, for 4 months in the case of SK-N-MC and IMR-32 cells and 6 months in the case of SH-SY5Y cells. During this period, no alterations in cell morphology, viability, or proliferative capacity were seen. All three neuroblastoma lines were negative for the CD4 receptor mRNA according to Northern hybridization and RNase protection assays. We conclude that HIV-1 produces persistent and inapparent infection in human neuroblastoma cells, using a CD 4-independent mechanism of entry to the cells.