This short review article on some pertinent observations in the unfolding story of interferon is dedicated to Professor Ilona Béládi on the occasion of her 80th birthday. This by no means covers the whole story on interferon. It just highlights some of the more striking findings made with interferon (or its inducers) over a time span of almost 50 years since its original discovery (in 1957) by Isaacs and Lindenmann. These observations concern (i) the induction of interferon by synthetic polyanions such as polyacrylic acid and polymethacrylic acid; (ii) the prolonged antiviral activity shown by polyacrylic acid in vivo; (iii) the interferon-inducing ability of double-stranded RNAs such as poly(I) x poly(C) and (iv) mismatched derivatives the...