Contact inhibition of replication of the established mammalian cell line 3T3 was examined during growth of the colony and compared with that of the Chinese-hamster cell line CHL-1. The growth curves of cells in the colonies conformed to the predicted exponential and linear rates for CHL-1 and 3T3 respectively. Autoradiographs of colonies in which DNA was labeled with tritiated thymidine showed that in 3T3 colonies, only peripheral cells were labeled, while CHL-1 colonies were labeled throughout.

In healthy volunteers, cetirizine does not prolong the QTc interval at doses of up to six times the usual recommended dose.

The major core protein of Mason-Pfizer monkey virus was purified by DEAE ion exchange column chromatography and shown to be 27,000 daltons (p27). Following the characterization of monospecific antisera prepared against p27, a radioimmunoassay was developed with these reagents and competition experiments were done with come of the recent M-PMY-like isolates as well as with other oncornaviruses. Results suggest that three of the viruses tested, AO, X-381 and FTP-1, are similar to M-PMV while J-96 virus is related, but not identical, to M-PMV. It is also shown that competition RIA can be used successfully to detect the presence of viral proteins in tissue homogenates and cell extracts.

Confluent 3T3 cultures make and release into the medium a diffusible factor which sustains the state of contact inhibition of replication. Evidence is given that the factor is a specific and reversible inhibitor of the RNA synthesis which precedes cellular replication.