A cDNA probe specific for type IV alpha 1 collagen gene gave no signal with normal muscle (NM), isolated larvae (L1), or at Day3 after infection. Messenger RNA was detected at Days 9 and 15, and both gave strong signals. A small background level of mRNA was noted at 8 months after initial infection. Similar results were obtained when a cDNA probe specific for type VI alpha 1 collagen was used. A cDNA probe specific for mouse 18S rRNA was weakly cross-reactive with parasite rRNA and demonstrated the presence of equivalent amounts of RNA in each lane. The nematode-specific 28S rRNA probe showed bands for each day of the infection. A shorter exposure time was used for lane 6 (L1 larvae) because of the large amount of rRNA present in the purified Trichinella RNA, compared to the synchronously infected samples.