When the paper was dissolved, Saeroen drifted into the film industry as a writer, making his debut with Albert Balink's Terang Boelan (1937).

He later established the daily Pemandangan with Oene Djunaedi, writing heated editorials with the pen name Kampret[2] (the Indonesian word for microbats).

[2] Around 1936 Saeroen was approached by Albert Balink and the Wong brothers to work on their new film collaboration, Terang Boelan (Full Moon), reportedly first only to improve the dialogue but later as the primary scriptwriter.

[8] After the success of Terang Boelan and Balink's emigration to the United States, much of the cast and crew – including Saeroen – were signed with Tan's Film.

In 1942 Saeroen wrote two works for Star Film:[16] Ajah Berdosa (Father Sins),[17] and Pah Wongso Tersangka.

[10] Over the next several years Saeroen continued to work as a journalist while opening several hotels in Cipayung with bat-themed names, including Kampret, Kalong (flying foxes[19]), and Kelelawar (roundleaf bats[20]);[2] he is also reported to have helped raise the children of Titien Sumarni after the actress' death.