The same probe, comprising two parallel wires, is used to measure either velocity or temperature derivatives in shearless grid turbulence at a Taylor microscale Reynolds number of about 40. The aerodynamic interference of the probe affects the mean velocity when the transverse separation Ay between the wires is smaller than about 3eta, where eta (similar or equal to0.4 mm for the present experiments) is the Kolmogorov length scale, but not the mean temperature. Spectra and corresponding moments of transverse velocity and temperature derivatives are significantly but similarly affected when Deltay less than or equal to 3eta, thus suggesting that this effect is more likely to be caused by electronic noise than aerodynamic interference. Indeed, after noise corrections are applied, the resulting derivative variances are brought into alignment with values inferred from two-point correlations with respect to y. Transverse derivative variances and their corresponding spectra satisfy isotropy closely but second-order structure functions satisfy it only when the separation is less than about 10eta, i.e. the dissipative range scales.