Digisonde sounders provide routine estimates of an ionosonde total electron content (ITEC) parameter that is taken to represent the vertical electron content of the ionosphere. The procedure involves integration under a profile, extrapolated to the topside from the measured bottomside by assuming an alpha Chapman layer with a constant scale height appropriate to that found just below the layer peak. The validity of the resultant ITEC parameter has been investigated here using measured height profiles of electron density from an incoherent scatter radar operated at a middle latitude site in the United Kingdom for several years around 1970. The data set of some 4000 profiles of electron density up to 700 km was used to determine statistically the relationship between the ITEC estimate and the measured total electron content calculated from the electron density observations. The results confirm that the ITEC method yields a generally reliable measure of the total content below 700 km, especially during nighttime, while in the daytime hours there is an overall tendency toward a small underestimate. An investigation of the differences between the modeled and measured densities with height in the topside, which are probably linked to the transition from O+ to H+ plasma, shows that during the day, excesses immediately above the peak may be compensated for at greater heights in the integration of the ITEC content.