TH~ erossl inking p roduced in po lymers b y ionizing rad ia t ion [1, 2] has a s t rong influence on the i r capac i ty to fo rm au tohes ion bonds dur ing seam welding. The comple te loss of weldabi l i ty of po lye thy lene (PE) films subjec ted to ~-radiat ion in air a t doses of 6-12 Mrad had been no ted [3]. The de te r io ra t ion of the au toand adhes ion capac i ty was also observed on sys t ems sub jec ted to vulcaniza t ion [4, 5]. The c rys ta l l in i ty of a p o l y m e r was also found to h inder the au tohes ion bond forming dur ing welding; this appea r s to be due to a lack of macroand v e r y res t r i c ted mic ro -Brownian m o v e m e n t of the molecules. Al though the influence of s t ruc tu re or c rys ta l l in i ty on the au tohes ion of po lymer s is of considerable impor tance , the quest ion has not been ful ly clarified. The s i tua t ion is made still more difficult b y the s t ruc tu ra l changes which occur dur ing welding itself, these being in addi t ion to the molecular crossl inking by i r rad ia t ion or vulcaniza t ion . The work r epo r t ed here deals wi th the effect of the e n u m e r a t e d fac tors on au tohes ion a n d the s t r eng th of the welding joint.