The effect of D-penicillamine on the replication of the Human Immunodeficiency Virus (HIV) in H9 T-lymphoblastoid cells was evaluated. HIV-infected and uninfected H9 cells were incubated for a period of 6 weeks with various concentrations of D-penicillamine. During the first 8 days, D-penicillamine (at concentrations of 0-150 micrograms/ml) did not influence growth and viability of H9/H9-IIIB cells. However, long term cultures and higher doses of the drug caused a decay in cell number and viability of the cultured cells. Up to the 8th day of culture, D-penicillamine did not exert an inhibiting effect on the number of HIV-infected cells but did suppress HIV-antigen production by up to 29%. After 6 weeks, in addition to a decrease of the relative viral antigen concentration from 390-500 ng/ml in the medium control to 210-320 ng/ml in cultures containing 150 micrograms D-penicillamine/ml, D-penicillamine also reduced the percentage of HIV-positive cells. Thus our results demonstrate an antiviral effect of D-penicillamine in H9 cultures.