TABLE 2.

Ratio of PFU to FFU^a

Virus	PFU/ml	FFU/ml	PFU/FFU ratio
vBSΔ27	<50	1 × 1010	NAb
vSM/TK-Δ27	7.8 × 105	7.8 × 109	0.0001
v27/TK-Δ27	1.2 × 109	8.1 × 109	0.14
HSV-1 KOS	2.8 × 109	2.0 × 1010	0.14

^aFFU were calculated at 7 h postinfection by immunostaining with an antibody reactive with ICP4.

^bNA, not applicable.