Balloon--borne measurements of the positive conductivity &sgr;+ from near ground level to 35 km are presented. The data were obtained in conjunction with measurements of the ionization rate q and the positive ion density n+. These three parameters are used to calculate the average positive ion mobility profile and the effective recombination coefficient profile. Within the experimental accuracy of about ¿10% the reduced mobility is consistent with altitude at a value of about 1.5¿10-4 m2 V-1 s-1. The recombination coefficient profile compares favorably to possible theoretical predictions, but there is some serious question as to whether the theoretical values can in fact be compared directly to the experimental results obtained here.