Most echoviruses reach higher titers in RD than in GMK-AH 1 cells, regardless of their passage history.

Stocks prepared in GMK-AH 1 cells of all 31 echovirus prototype strains were titrated simultaneously from identical dilution series in tube cultures of RD and GMK-AH 1 cells. 14 types reached titers 10 to 60 times higher in RD than in GMK-AH 1 cells. 10 other types titered 4 to 6 times higher in RD than in GMK-AH 1 cells. Three prototypes only (Nos. 1, 8 and 9) titered considerably lower in RD than in GMK-AH 1cells. Echovirus types 22 and 23 did not replicate in RD cells. Stocks of the various echoviruses prepared in RD cells mostly gave titer differences between RD and GMK-AH 1 cells similar to those of corresponding stocks from GMK-AH 1 cells.