Did not write any letters between April 1689 and mid-September 1691

Between April 1689 and mid-September 1691, Leeuwenhoek did not write any letters with scientific observations. This eighteen months was the longest period of his life without a letter until 1718-1719. It period came in the middle of the years when astronomer and Philosophical Transactions editor Edmond Hally declined to publish any articles about microscopic observations, not just Leeuwenhoek's.

In addition, Leeuwenhoek did not issue any of his Dutch or Latin self-published volumes during this time.

He did, however, continue his personal correspondence, of which we have only one example, his exchange of letters with Christiaan Huygens, Letter L-207 and Letter L-208.