  Using precise measurements of the helium D3 line, we have searched for
statistically significant variations in the strength of chromospheric activity
in 13 early F-type stars and two late F-type stars. In two early F-type stars,
we find short-term (hours to days) variability based on ~25 observations over
the course of a week. In an additional two cases we find significant
differences between observations taken years apart, but we can most likely
explain this apparent long-term variation as an artifact of probable short-term
variations. The evidence suggests that pure rotational modulation of discrete
active regions is not responsible for the short-term variations in the early
F-type stars and that either a more global process is at work, or we are seeing
large number of small active regions spread across the star. In contrast, the
two late F-type stars in the sample show strength and/or wavelength variations
that are consistent with "solar-type" activity typified by the rotational
modulation of active regions. Our results suggest that variability does not
cause the wide range in activity levels observed within the early F-type stars.
