We have measured the resistive transitions of c-axis oriented YBCO thi
n films in applied magnetic fields for both H parallel-to ab planes an
d H parallel-to c axis up to 8T. We have analyzed the data using the 3
D fluctuation theory of Ullah and Dorsey, and found a good fit to the
predicted scaling function above and below the onset of the transition
. The deduced Tc(H) is linear in all the field range, and the extracte
d dHc2/dT values for both of the field orientations are very close to
the accepted one, i.e. -(dHc2/dT)=(1.4-1.8) T/K for H parallel to the
c-axis (1.4 T/K is the slope derived for one sample and 1.8 T/K is the
slope for two other samples) and 10(T/K) for H parallel to the ab pla
nes. For H parallel-to c, the upper critical field slopes from the flu
ctuation conductivity agree very well with the slopes estimated from t
he midpoints of the resistive transitions.